This paper investigates the determinants of game-day attendance in the Chinese Professional Baseball League (CPBL) from 2001 to 2007. We include measures of league-level uncertainty and game uncertainty for two rivals at the same time in a quantile regression model. The results support the hypothesis of outcome uncertainties. Closer wins by the competing teams within a league and a smaller gap in terms of the winning percentage between two teams induces more outcome uncertainty, and consequently leads to higher attendance. Moreover, the results of the quantile regression show that these effects are especially enhanced in high box-office (high quantile) games. These results hold for different measures of competitive balance. Other factors such as the quality of play and the Derby effect also significantly influence game-day attendance. Moreover, the transportation cost of a game is less important in a league with a high density of stadiums.