The present study aimed to investigate the predictability of five factor personality traits by adult attachment styles. The statistical sample of this research included 240 students studying at University of Hormozgan during the educational year 2011-2012 who were selected using availability sampling from among all students and responded to two questionnaires: Relationships Scales Questionnaire (RSQ) and the Five Factor Personality Traits Questionnaire (NEO). The results of the regression analysis showed that secure attachment style can predict neuroticism inversely, while positively predicting extroversion, openness to experience, agreeableness, and conscientiousness. Preoccupied attachment style also plays a role in predicting agreeableness inversely. In addition, conscientiousness is directly predicted by fearful attachment style and reversely by negating attachment style (P<0/001).