Purpose-Investors benefit from a large number of information resources in order to maximize their earnings from financial instruments they have invested. One of the resources that investors benefit from is financial ratio information which they obtain by analyzing firms' financial statements. Accordingly, the aim of this study is to determine if there is a relationship between stock prices and profitability ratios which take place in financial ratios and also to analyze if profitability ratios can be directive indicator while investing in stocks with the aim of maximizing earnings. Methodology-In this research, panel data regression analysis was applied between lagged stock prices of firms in ISE100 and their profitability ratios including gross profit margin, operating profit margin, net profit margin, return on asset and return on equity. Once we had decided that fixed effects model is convenient for our research, the model was estimated by Driscoll-Kraay Estimator which produce robust standard errors. Findings-According to result of our analysis, it was determined that there is a positive linear relationship between firms' net profit margin and their stock prices. Conclusion-It was concluded that while making investment decisions, taking net profit margin into consideration can contribute to investors' earnings.