In this study, Markovitz's modem portfolio theory (MPT) and traditional portfolio theory (TPT) are examined empirically on the Istanbul Stock Exchange in terms of their results. For this purpose, 230 stocks, which have weekly price data, were used between 2003-2008 and 2012-2017. The portfolio created by MPT and TPT is compared with Sharpe performance criterion according to the actual results. As a result, it has been determined that portfolios created by MPT do not produce better results than portfolios formed by TPT. This result was valid both on bull and bear markets. The average actual Sharpe ratios of portfolios on bear markets are respectively -0,79 and -0.78 for portfolios created with mean variance model and traditional model. The difference between the averages was not statistically significant. On the bull markets, the same rate were 0.24 for the traditionally generated portfolios; for portfolios created by the mean variance model, it is 0.15 and the difference between the mean values is not statistically significant. Hovewer, expected sharpe ratio of portfolios formed by mean variance method are greater than those of portfolios formed by TPT and differences between them is statistically significant.. This result are consistent with the results of studies in the literature.