Abstract Introduction Research has found relationships between sleep quality and personality traits. Poor subjective sleep quality has been observed within individuals scoring high in Neuroticism and low in Conscientiousness. Personality traits have also been associated with cognitive functioning and the link being worse cognition and poor sleep quality is established. However, less is known regarding the role of cognitive functioning in the relationship between personality and sleep quality, particularly in aging populations. This study investigated whether subjective cognition acted as a mediator between individual personality traits and subjective sleep quality in middle-aged and older adults. Methods Middle-aged and older adults (N=269; Mage= 64.5, SD=7.8; 123 women/146 men) who were cognitively healthy completed an online survey through Qualtrics measuring demographics, personality (Big Five Inventory-10; BFI-10), self-reported sleep (Pittsburgh Sleep Quality Index; PSQI), and subjective everyday cognition (Cognitive Failures Questionnaire; CFQ). Separate mediation analyses using SPSS PROCESS macro [and testing for indirect effects using 5,000 bootstrapped samples and 95% Confidence Interval (CI) and controlling for conditional associations among all pathways] examined whether subjective everyday cognition (CFQ scores) mediated the relationship between different personality traits (BFI-10 Conscientiousness and Neuroticism scores) and self-reported sleep (PSQI-Total Score), controlling for age and sex. Results Neuroticism and PSQI-Total Score was partially mediated by CFQ. There was a significant association between Neuroticism and total PSQI (total effect=0.588, SE=0.110, p<0.001). There were positive associations between Neuroticism and CFQ (a-path effect=2.765, SE=0.383, p<0.001) and CFQ and PSQI (b-path effect=0.068, SE=0.017, p<0.001). The indirect effect was significant (effect=0.187, SE=0.054, 95% CI=0.088 to 0.301). There was no association between Conscientiousness and PSQI-Total Score (total effect=-0.123, SE=0.133, p=0.358), therefore mediation analysis (testing of CFQ as a mediator) was discontinued. Conclusion In middle-aged and older adults, subjective everyday cognition mediates the relationship between Neuroticism personality trait and self-reported sleep quality. Individuals scoring higher in Neuroticism report worse subjective sleep quality as their subjective cognitive failures increase. Findings underscore the interacting roles of personality and everyday cognition on perceived sleep. Clinicians should consider individual personality profiles (via personality assessments) and subjective everyday cognitive ratings for a better understanding of the factors impacting middle-aged and older adults’ sleep profiles. Support (if any):