Objectives: The aim of this study was to examine the relationships between domains and facets of the five factor model of personality and happiness, mental health and physical health. Method: In a descriptive study, 359 individuals (177 females and 182 males) were chosen through multi-stage stratified random sampling procedures from the population of undergraduate students from two universities in the city of Tehran (Iran). The subjects completed the Revised NEO Personality Inventory and three individual rating scales (happiness, mental health and physical health). Data were analyzed using Pearson correlation coefficient and stepwise regression analysis. Results: Happiness and physical health were positively related to extraversion and conscientiousness and negatively related to neuroticism. Mental health was positively related to extraversion, agreeableness and conscientiousness and negatively related to neuroticism. In addition, happiness was positively associated with mental and physical health. Stepwise Regression analysis showed that happiness and physical health were predicted by neuroticism, openness to experience and extraversion. However, only some facets of each factor were significant predictors of the factors. Conclusion: Along with other studies findings, high extraversion and low neuroticism are major predictors of happiness, mental health and physical health.