The purpose of this study was to examine whether changes in stock price behavior occurred in the Korean stock market due to changes in investors' perceptions of accounting information following the opening of the stock market to foreign investors. The empirical results revealed that after the stock market opening, the co-movement phenomenon of stock price fluctuations by industry sector decreased, and the degree of differentiation in stock price levels increased. As factors explaining the degree of stock price level differentiation, the influence of accounting figures such as net income and net book value of assets generally increased, with the influence of net book value of assets notably growing compared to the pre-opening period. Furthermore, after the stock market opening, the explanatory power of accounting earnings levels and accounting earnings changes as variables explaining stock price fluctuations improved significantly. These empirical results support the basic hypothesis of this study that investors' perceptions of accounting information improved after the stock market opening. The cause of this perceptual change appears to be largely attributable to the role of foreign investors who employed fundamental investment analysis techniques during the early period of stock market opening. This study carries various policy and academic implications by empirically demonstrating the change in investors' perceptions of accounting information in the stock market.