This thesis investigates the information content in the trading volume in the option market relative to the trading volume in the stock market. First of all, we examine the predictive ability of O/S ratio about the future volatility of stock market. Next, we construct the non-market maker O/S net demand for volatility to predict the stock market volatility to improve the predictive ability of O/S ratio. Our empirical results show non-market maker O/S net demand for volatility has better predictive ability than O/S ratio, and foreign investors exhibit the best predictive ability for the stock market volatility in next day, among different categories of traders. This evidence reveals that foreign investors seem to have informational advantage in the trading of Taiwan stock market.