This paper investigates the effect of online sales on stock price synchronicity using the unique data of Chinese listed companies' online sales from e-commerce platforms. We document three notable findings. First, online sales are negatively associated with stock price synchronicity, suggesting that online sales facilitate the incorporation of firm-specific information into stock prices. Second, online sales reduce stock price synchronicity through analyst coverage and media coverage. Third, the synchronicity-reducing effect of online sales is stronger in firms with a lower urban Internet development level, a more competitive product market, and a worse earnings quality. Overall, our analyses suggest that online sales are an important determinant of stock price synchronicity.