This research was performed in order to validate the Narcissistic Personality Inventory (NPI-40) from Raskin and Terry (1988) in an Iranian population. In this cross sectional survey, 335 university students of three departments, selected in stratified sampling method, were assessed by the Narcissistic Personality Inventory-40 (NPI-40), The Neuroticism Extroversion Openness Inventory (NEO-FFI) and the Millon Clinical Multi-axial Inventory-III (MCMI-III). The concurrent validity was assessed through completing a simultaneous MCMI-III test, while the differential validity was assessed as the differential power of test between individuals who had high or low extroversion and high or low agreeableness factors. Test-retest, splitting and internal consistency coefficients were reported. There were significant correlations between NPI-40 and MCMI-III scores (a=0.83, p<0.000). The reliability of NPI-40 was proved (p=0.005). Test-retest consistency coefficient, splitting consistency coefficient and Cronbach alpha coefficient for internal consistency were estimated to be 0.72 (p<0.000), 0.75 (p<0.05) and 0.65 (p<0.05) respectively. The Goodness of Fit Index for the 7 factors of the NPI-40 has been acceptable. Conclusion: Based on the results, the NPI-40 with 7 factors is an appropriate instrument to screen narcissistic personality traits in Iranian population for pertaining researches, and is a diagnostic tool in nonclinical population.