When the Islamic world is investigated, it is seen that capital markets are not developed sufficiently in many countries. In this context, the factors affecting the development of capital markets in 21 out of 57 member countries of the Organization of Islamic Cooperation were analyzed using data for 1981-2018 period by applying panel data analysis. In this study, capital market development variable is represented by the stock market capitalization ratio. Hausman test was used to choose between fixed effects and random effects. Hausman test results indicate the best estimator for the model is random effect. In addition, there was no autocorrelation problem. Due to the existence of a heteroscedastic problem, a robust test was performed to solve it. Robust test findings show that, fixed capital formation, market liquidity, exports, and corruption control rate variables positively affect the capital market development. However, capital market development was negatively affected by the savings rate, and market turnover variables.