Theory and research have suggested that recurrent daily experiences can affect personality traits. The present study examined the longitudinal relation between individual differences in positive daily experiences and the Big Five personality traits. Data came from Dutch mothers (N = 483; M age = 44 years at T1) who completed up to six yearly personality questionnaires and 15 between‐year assessment bursts, lasting five consecutive days each. Using multilevel structural equation modelling, we found that individual differences in daily experiences of positive affect and perceived relationship support/affection with partners and children were positively associated with subsequent rank‐order changes in all Big Five personality traits. In contrast, we found little evidence that personality traits were associated with rank‐order changes in daily experiences, which may be due to the very‐high rank‐order stability of positive affect and relationship support. Furthermore, positive daily experiences demonstrated incremental validity in predicting rank‐order changes in trait agreeableness, emotional stability, and openness, over and above daily negative affect and relationship conflict. The results suggest that positive affective and interpersonal daily experiences contribute to positive personality trait changes in middle adulthood. We discuss these results in the context of contemporary theories of personality trait development.