This study aimed to assess the mediating effect of phenomenal or perceptual field on the relationship between self-concept and nutrition behavior based on Rogers ' client centered personality theory. Previous studies have failed to take into account the mediating role of perceptual field in the study of such relationship. As Rogers suggested self-concept is not a direct determinant and organizer of behavior (in this case nutrition behavior), but it is determined by the perceptual field involved in such behavior (in this instance health perception and knowledge). The hygienic lifestyle of 505 (347 male and 158 female) undergraduate students selected through random cluster sampling was measured using a self report questionnaire adapted from Smith and Maurere (2000). This questionnaire consists of 50 questions on a Likert scale. Structural equation modeling was used to analyze the data. Results showed that the path coefficients of self-concept over perception of health was 0.37 and perception of health over nutrition behavior was 0.90 (p< 0.01) respectively. However, the same value for a direct elation ship between self-concept and nutrition behavior was -0.03, thus being statistically insignificant. Results showed the importance of perception about health as a mediating variable in relationship between self-concept and nutrition behavior.