The aim of this study was to determine the effect of expressive writing on sexual self-concept in men with multiple sclerosis. It was registered in IRCT with the code IRCT20211028052892N1 on 17/11/2021. The study was a randomized controlled clinical study conducted on 70 men attending an MS clinic in Tehran in 2022. The participants were randomly assigned to intervention and control groups. For two weeks, participants in the intervention group disclosed their emotions and expressed their feelings in writing twice a week. Sexual self-concept was evaluated using the Multidimensional Sexual Self-Concept Questionnaire on three occasions. Data analysis was performed using SPSS V22. Based on the results of Generalized Estimating Equations, there was a statistically significant difference only in the area of internal control of sexual issues in the intervention group after the completion of the written intervention (p = 0.046). However, there was an increase in the area of fear of sexual intercourse after the completion of the intervention, in both groups (p = 0.017). Nevertheless, there was no statistically significant difference in the mean of positive and negative sexual self-concept in the two groups (P = 0.756 and P = 0.334). In general, written expression was able to make a significant difference in some subscales of sexual self-concept dimensions.