The purpose of this study was to investigate the construct validity of the Assessment and Development Center of Managers in the National Iranian Oil Company. The research method is based on the applied purpose and in terms of data collection is descriptive-analytical. The statistical sample includes data obtained from the evaluation of 384 managers who were selected from the database of managers by simple random sampling. These data were analyzed based on the multi-trait-multi-method and the confirmatory factor analysis. The overall fit indices showed that the data fit the model very well. The examination of the individual parameter estimates indicates that while both dimension and exercise factors contribute to the ratings, the estimates for exercise parameters are substantially larger in all cases than estimates for dimension factors (mean parameter estimates of .39 and .68 for the dimension and exercise parameters, respectively). In addition, inter-correlations among the latent dimension factors ranged from 0.98 to 1.0, providing evidence of no discriminant validity across dimensions. Thus, these results support and are consistent with those obtained from the correlational analyses. To put it short, the exercise factors are the primary determinants of assessment center ratings.