The research purpose is to investigate the relationship between happiness, personality traits (introversion and extroversion) and mental health among the university students of IAU, Science and Research Branch. For this purpose, 364 students (181 male and 183 female) were selected using multi- stage cluster sampling. The tools employed to gather data were the personality traits (introversion and extroversion) questionnaire, mental health and Oxford & Argil happiness questionnaires inventory. The data analyzed by multi- variable regression analysis showed that there is a significant correlation between demographic variables (age, sex, educational level, number of children) and happiness; this was the case also between psychological variables (introversion and extroversion) and comfort with the self, others; and between mental health and happiness. The variable of extroversion was a predictor to happiness through mental health.