en Evaluation of the Effectiveness of Acceptance and Commitment Based Therapy on Psychological Hardiness, Social Isolation and Loneliness of Women with Breast Cancer psychology پژوهشي Research <strong>Background:</strong> There are alternative and complementary approaches for general health issues and palliative care for women with breast cancer. The current paper aimed at evaluating the effectiveness of acceptance and commitment therapy (ACT on psychological hardiness, social isolation and loneliness of women with Breast Cancer.<br> &nbsp;<br> <strong>Method</strong>:&nbsp; This was a quasi-experimental study with a pretest, posttest and 8-week follow-up with a control group. The statistical population included all women with breast cancer referred to the cancer ward of Shohada Tajrish Hospital in Tehran in 2020. &nbsp;30 subjects in the study were selected through purposive sampling assigned to two groups of 15 people (experimental and control). The experimental group underwent acceptance and commitment therapy interventions for 8 sessions of 90 minutes and the control group did not receive any intervention. Data were collected using Lang and Goulet Psychological Hardiness Scale, Social Isolation Questionnaire and The UCLA Loneliness Scale and ANOVA with repeated measures was used to test the research hypotheses.<br> <strong>Results:</strong> The demographic characteristics included age (34,23 &plusmn;6,12), marriage length (8.46 &plusmn; 5,14), number of children (1&ndash;4 children) and education level (high school graduation = 10, bachelor degree = 9, MA/MS = 9, Ph.D. = 2). &nbsp;Based on the findings, the difference between the scores of psychological hardiness (P <0.01), social isolation (P <0.01), and the variable of loneliness (P <0.01) in the three stages of the study is significant. &nbsp;Also, the mean scores of all research variables in the experimental and control groups were obtained significantly (P <0.01). The results show that about 13.3%, 24.1%, and 60.7% of the individual differences in the variables of psychological hardiness, social isolation, and loneliness are related to the differences between the two groups, respectively.<br> <strong>Conclusion</strong>: According to the results, it seems that acceptance and commitment therapy is effective in increasing psychological hardiness, reducing social isolation and loneliness of women with breast cancer, and the use of this treatment method on the variables was beneficial and effective.&nbsp;<br> &nbsp; <div style="text-align: justify;"><strong>Background and objectives:</strong> There are alternative and complementary approaches for general health issues and palliative care for women with breast cancer. This study aimed at evaluating the effectiveness of acceptance and commitment therapy (ACT) on psychological hardiness, social isolation, and loneliness of women with breast cancer.<br> <strong>Methods</strong>: This was a quasi-experimental study with a pretest-posttest design. The study population consisted of all women with breast cancer who had been referred to the oncology ward of Shohada Tajrish Hospital in Tehran (Iran) in 2020. Thirty subjects were enrolled via purposive sampling and then assigned to an experimental group (n=15) and a control group (n=15). The experimental group received eight sessions of ACT interventions (90 minutes a session), and the control group did not receive any intervention. The subjects were followed-up for eight weeks after the last ACT session. Data were collected using the Lang and Goulet Psychological Hardiness Scale, Social Isolation Questionnaire, and the UCLA Loneliness Scale. The collected data were analyzed using repeated measures ANOVA.<br> <strong>Results:</strong> The mean age of subjects and mean duration of marriage were 34.23&plusmn;6.12 years and 8.46&plusmn;5.14 years, respectively. &nbsp;Based on the findings, the mean scores of psychological hardiness (p=0.005), social isolation (p=0.001), and loneliness (p=0.001) differed significantly between the study groups in the posttest stage. &nbsp;<br> <strong>Conclusion</strong>: According to the results, it seems that ACT is effective in increasing psychological hardiness and reducing social isolation and loneliness of women with breast cancer.&nbsp; &nbsp;&nbsp;</div> Acceptance and Commitment Therapy (ACT), Psychological Hardiness, Social Isolation, Loneliness, Breast Cancer Acceptance and Commitment Therapy, Psychological Hardiness, Social Isolation, Loneliness, Breast Cancer 1 10 http://jcbr.goums.ac.ir/browse.php?a_code=A-10-275-1&slc_lang=en&sid=1 Roshanak Namazi rahanr368@yahoo.com 10031947532846003775 10031947532846003775 No Department of Psychology, Science and Research Branch, Islamic Azad University, Alborz, Iran Soolmaz Bolook Sahragard soolmaz_bolook@yahoo.com 10031947532846003776 10031947532846003776 No Department of Psychology, Faculty of Psychology, Islamic Azad University of Tehran Markaz, Tehran, Iran Hoda Pourkaveh hoda.pourkaveh@gmail.com 10031947532846003777 10031947532846003777 No Tehran Medical Branch, Islamic Azad University, Tehran, Iran Shariat Homayoon Shariat Homayoon@gmail.com 10031947532846003778 10031947532846003778 No Department of Psychology, Shiraz Branch, Islamic Azad University, Shiraz, Iran Seyyed Kamal Mirniyam mirniyamkamal@gmail.com 10031947532846003779 10031947532846003779 Yes Department of Psychology, Khorasgan Branch, Islamic Azad University, Isfahan, Iran javad seyed jafari Javad_jafari90@yahoo.com 10031947532846003780 10031947532846003780 No Allameh Tabataba'i University, Tehran, Iran