This study was conducted to investigate the relationships of personality traits (agreeableness, conscientiousness and neuroticism) and organizational justice with mediating role of negative affect. Participants were 227 nurses from the hospitals of social security organization in Isfahan province were selected by simple random method. The instruments consisted of Organizational Justice Questionnaire (Colquitt, 2001), NEO Personality Inventory (McCrae & Costa, 1985) and Job-related Affective Well-being Scale (Van Katwyk, Fox, Spector, & Kelloway., 2000). The indirect effects were tested using the Bootstrap procedure in Preacher and Hayes (2008) SPSS Macro program. Results indicated that neuroticism correlated significantly with Procedural, distributive, interpersonal and informational justice (P<0.01). Agreeableness and conscientiousness significantly correlated only with procedural, distributive, interpersonal and informational justice (P<0.01). Also, negative affect mediated the relation between personality traits and organizational justice. While considering the limitations, discussion and implications of the results are also presented.