Background: Human immunodeficiency virus (HIV/AIDS) is the factor causing AIDS. The virus is categorized into retroviruses that attack and destroy the immune system of the body and cause lethal infections. Objectives: The present study aimed to investigate the effectiveness of mindfulness-based cognitive therapy in the improvement of sleep quality and perceived social support of the patients with HIV/AIDS. Methods: The present study is randomized controlled trial research. The study population included individuals with HIV-AIDS from Ahvaz county's center of behavioral disease counseling. The study sample volume consisted of two groups, named mindfulnessbased cognitive therapy and control groups, each one contained 15 individuals who were selected randomly. The experimental intervention was undertaken during eight 1.5-hour sessions that were held once a week. To gather the data, the sleep quality scale, perceived social support questionnaire, SCL-90-R scale, and demographic factors questionnaire were used. Multivariate covariance analysis and SPSS-22 Software were utilized for analyzing the data. Results: In terms of gender, the experimental group consisted of 8 (53.3) women and 7 (46.7) men. In the control group, 4 (26.7) were women and 11 (73.3) were men. The mean (standard deviation) age of the participants in the experimental group was 35.7 (7.42) and the mean (standard deviation) of the age of the control group was 37.8 (9.1). The results showed that mindfulness-based cognitive therapy had a significant effect on sleep quality (F = 27.98, P < 0.001) and perceived social support (F = 36.20, P < 0.001) in patients with HIV/AIDS. Conclusions: It can be concluded that mindfulness-based cognitive therapy is effective in improving the sleep quality and perceived social support of patients with HIV/AIDS. Based on the results of this study, it seems that by teaching mindfulness-based cognitive therapy, patients' sleep quality and perceived social support can be reduced.