Attending university can be very stressful as students have to go through the process of adapting to new educational and social environments; this experience of difficult change affects student's psychological wellbeing and subsequently their success in academics. This study examines personality characteristics, psychological wellbeing and academic success among Nigerian undergraduates. While cross sectional design and convenient sampling method were employed, 214 undergraduates were sampled. A structured questionnaire focusing on sociodemographic information, personality profile, psychological wellbeing and academic success was administered to the participants. The data were analyzed using descriptive and inferential statistics. The result reveals that agreeableness, conscientiousness and openness to experience had a significant positive relationship with psychological well-being, while agreeableness, conscientiousness and openness had positive relationship with academic success; meanwhile, neuroticism had negative relationship with academic success. Furthermore on a regression model, personality characteristics did not independently but jointly predicted psychological wellbeing. Meanwhile personality characteristics independently and jointly predicted academic success. The study conclude that student's personality characteristics are important for sound psychological wellbeing and effective academic success among Nigerian undergraduates.