This study aims to evaluate the functionality and impact of portfolio management in investment companies actively operating in the Tehran Stock Exchange between 2005 and 2010. The assessment is based on modern and post-modern portfolio theories using Sharpe, Sortino, and Sterling ratios. The first hypothesis was tested through statistical analysis of variance (ANOVA) and pairwise mean comparisons using the LSD pre-test. The results indicate that the performance of investment companies varies according to the Sharpe, Sortino, and Sterling ratios, with Sterling’s ratio showing a slightly better performance. The second hypothesis compared the performance of investment companies to the overall market. Except for the Sortino ratio, the other metrics demonstrated that investment companies performed better than the market. Finally, the results of the Kruskal-Wallis test and Chi-Square statistic confirmed that all three ratios provide consistent rankings of investment companies.