This paper investigates whether seasonalities in daily stock returns are related to the trading behavior of individual and institutional investors. The change in the investor structure of B-share markets in Shanghai and Shenzhen after the abolition of ownership restrictions in 2001 provides a unique testing environment. We show that day-of-the-week effects are attenuated after the market entrance of Chinese individual investors, who had previously not been allowed to trade in B-shares. Our empirical results suggest that institutional rather than individual investors are a main driving force behind such anomalies. In addition, we find evidence of reduced index return autocorrelation and US spillover effects in the post-liberalization period.