The present study aimed to determine the effectiveness of mindfulness-based stress reduction as one of the effective and new methods in improving cognitive flexibility and sleep quality in the elderly. It was a quasi-experimental study with pretest, posttest and control group design. The statistical population of the study included all elderly men in Dezful in 2018. The samples of this study consisted of 30 men elderlies (60-70 Ages) who were selected through available sampling and according to inclusion criteria. The experimental group received eight ninety-minute sessions during two months while the control group didn’t receive this intervention during conducting the study. The applied questionnaires in the study included [1] Pittsburgh Sleep Quality Index (PSQI) and Cognitive Flexibility Scale. Data were analyzed using univariate analysis of covariance. The findings showed that mindfulness-based stress reduction could significantly improve cognitive flexibility and sleep quality. based on the findings, it can be concluded that mindfulness-based stress reduction can be considered as an effective intervention to improve cognitive flexibility and sleep quality in the elderly men.