Investigation of seasonal dynamics of culturable bacterium (CB) numbers in freshwater bodies is essential in understanding the bacterium response to various class quality water systems, and subsequently should provide critical knowledge on the bioremediation of contaminated water. In this study, eight representative freshwater bodies in Beijing were selected which can be categorized into four different water quality levels (Ⅱ, Ⅲ, Ⅳ, and Ⅴ). Among these water bodies, Tuancheng lake, Kunming lake, Yuyuantan lake, and Beihai lake were regarded as low pollution sites, because the water quality in the sites were better than Ⅲ-class standards during the most time of a year. However, Taoranting lake, Zizhuyuan lake, Longtan lake, and Tonghui river were regarded as highly contaminated sites, because the water quality in these sites were worse than Ⅳ-class during the most time of a year. The seasonal dynamics of CB numbers in the eight freshwater bodies were investigated using culture method from August 2008 to July 2009. The results indicated that CB numbers were lowest (4.72±6.37) in February and highest (8.04±3.72) in August. The total average numbers of culturable bacteria from high to low were 6.68±1.91 in summer (Jun.-Aug.), 6.60±2.10 in autumn (Sept.-Nov.), 5.80±2.33 in winter (Dec.-Feb.), and 4.90±2.04 in spring (Mar.-May). The average culturable bacteria numbers were significantly lower in spring than that in summer and autumn, but there were no significant difference of BN number between spring and winter and among the summer, autumn and winter. There was a statistically significant positive correlation between the CB numbers and temperature. CB numbers were elevated with the increase of water quality class, and CB numbers reached the highest in Ⅴ-class water quality sites. On the other hand, no significant difference in CB numbers among the Ⅱ-, Ⅲ- and Ⅳ-class water quality sites. CB numbers were positively correlated with water quality class. There was a significant seasonal dynamics of CB numbers in low pollution sites with Ⅱ- and Ⅲ-class water quality, but not in high pollution sites with Ⅳ- and Ⅴ-class water quality. The average numbers of culturable bacteria in low pollution sites were 6.54±2.06 in summer, 6.33±1.73 in autumn, 4.75±1.83 in winter, and 4.26±1.09 in spring. Two ranges could thus be divided in terms of numbers into high (6.54-6.33, summer and autumn) and low (4.75-4.26, winter and spring), and the difference between high and low ranges was statistically significant. However, no significant difference exists within high range seasons (spring and winter) and low range seasons (summer and autumn). In comparison, the average numbers of culturable bacteria in highly contaminated sites were 6.86±2.32 in autumn, 6.85±2.39 in winter, 6.82±1.83 in summer, and 5.52±2.58 in spring. No significant difference was observed in terms of average culturable bacteria number among spring, summer, autumn, and winter. CB numbers were positively correlated with temperature for the Ⅱ- and Ⅲ-class water quality sites, but no significant correlation between CB numbers and temperature for Ⅳ- and Ⅴ-class water quality sites. The results demonstrated that the CB numbers were significantly influenced by temperature and water quality.