Background: There is a bidirectional relationship between marital discord and chronic disease. Considering its importance to individuals with chronic diseases, it is critical to explore the factors that influence marital adjustment. This study aimed to investigate the relationship between irrational beliefs and marital adjustment among couples with chronic diseases in Bushehr, Iran. Methods: This descriptive correlational cross-sectional study investigated 92 couples (including 184 individuals) in which at least one spouse had one or more of the most common chronic diseases. Participants were selected using a convenience sampling method from internists' and cardiologists' offices, specialty clinics, and comprehensive healthcare centers in Bushehr during 2022. Data were collected using a demographic survey, the Dyadic Adjustment Scale developed by Graham B. Spanier and the short-form of Jones Irrational Beliefs Questionnaire (IBQ). Data were analyzed using descriptive statistics, Pearson correlation, and univariate and multivariate hierarchical linear regression tests using SPSS-20 software. A significance level of p<0. 05 was considered for all analyses. Results: The mean and standard deviation of the total irrational belief scores for women and their husbands were 111. 21±23. 60 and 105. 24±25. 24, respectively. Furthermore, the mean marital adjustment score of the couples was 102. 50±18. 36. Additionally, 38% of the couples had marital discord. No significant correlation was found between the women’s irrational belief domains and their marital adjustment. However, regarding men's irrational belief domains, "feeling helpless against change" showed a significant negative relationship with marital adjustment (β=-0. 400,CI95%:-0. 703,-0. 083). Conclusion: The results showed that men's beliefs influenced the marital adjustment of couples. Therefore, when counseling couples experiencing marital discord, especially those with chronic diseases, the psychologists and family counselors need to identify the factors affecting it. For instance, men's irrational beliefs, especially feeling helpless against change is an affecting factor that can be reduced through appropriate counseling