Online learning environments have become increasingly prevalent in higher education, necessitating an understanding of factors influencing student engagement. This study examines the mediating role of self-regulated online learning in the relationship between five-factor personality traits and student engagement among university students. A sample of 437 university students from educational sciences, social sciences, and health sciences disciplines participated in the study. Data were collected using 'The Big Five Inventory' to assess personality traits, the 'Self-Regulated Online Learning Questionnaire' to measure self-regulated online learning, and the 'Student Engagement Scale in the Online Learning Environment' to evaluate student engagement. Structural equation modeling with bootstrap analysis was employed to analyze the data. The study findings indicate that the five factor personality traits significantly predict self-regulated online learning. Furthermore, self-regulated online learning is a significant predictor of students' engagement in the online learning environment. Additionally, the five factor personality traits are found to be significant predictors of student engagement in the online learning environment. Lastly, self-regulated online learning plays a partially mediating role in the relationship between the five factor personality traits and student engagement in the online learning environment. This study underscores the importance of considering individual differences in personality traits and fostering self-regulated learning strategies to enhance student engagement in online learning environments. Understanding these dynamics can inform the design of effective interventions aimed at improving student outcomes in online education.