Background: Cancer can change patients' physical appearance and thereby, threaten their psychological well-being. The current study aimed to evaluate the effects of mindfulness-based cognitive therapy on the dysfunctional beliefs and the social appraisal of the patients with cancer and changes in physical appearance. Methods: It was a pretest-posttest controlled quasi-experimental study. A convenience sample of 40 patients with skin, breast, head and neck cancers was recruited from Shahid Ghazi Hospital, Tabriz, Iran. The patients had cancer-induced changes in physical appearance such as severe hair and eyebrow loss, mastectomy and skin lesions. They were randomly allocated to the experimental (20 patients) and the control groups (20 patients). Patients in the experimental group received mindfulness-based educations in eight 1.5-hour sessions held twice a week in four consecutive weeks while patients in the control group received no education. Before and one week after the study intervention, patients in both study groups completed the Jone irrational belief test and the social appraisal subscale of the self-talk scale. The data were analyzed by the SPSS ver. 16.0 and through conducting the independent-and the paired-sample T-tests and the multivariate analysis of variance (MANOVA) at the significance level of 0.05. Results: Study findings revealed that mindfulness-based cognitive therapy significantly improved the participating patients' demand for approval, high self-expectation, blame proneness, frustration reactive, emotional irresponsibility, anxious over-concern, problem avoidance, perfectionism, social appraisal (P < 0.001), dependency and helplessness for change (P < 0.05). Conclusions: Mindfulness education is recommended to correct dysfunctional beliefs and improve social appraisal of patients with cancer and changes in physical appearance.