Abstract: To examine temporal and spatial changes of bacterial communities in the Wenyu River at Beijing, China, water and sediment samples were collected in wet and dry seasons from eleven sites. Quantification of total bacteria (TB), ammonia-oxidizing bacteria (AOB) and denitrifer genes (nosZandnarG) were performed by real-time PCR. The copy numbers of the total bacteria 16S rRNA fragment were in the range of 1.05×10⁹-7.38×10¹¹ copies/L in the wet season and 1.06×10⁹-2.69×10¹² copies/L in the dry season respectively. The AOB copy numbers in the wet and the dry season were nd-4.11×10⁸ and nd-1.15×10⁹ copies/L respectively. The copy numbers of nosZandnarGgenes were nd-2.37×10⁸ and 3.61×10⁸-1.13×10¹⁰ copies/L in the wet season, while they were 2.0×10⁶-3.04×10⁹ and nd-1.39×10¹⁰ copies/L in dry season respectively. For sediments collected in the dry season, the copy numbers of TB, nosZand narGgenes were 1.35×10⁹-7.32×10¹⁰, nd-1.06×10⁷, and 1.99×10⁷-1.02×10⁸ copies/g. The TB copy numbers in the dry season were slightly higher than those in the wet season, while the AOB copy numbers were much higher in the dry season than in the wet season due to high concentration of ammonia nitrogen. Pearson correlation analysis showed no significant relationship between the bacteria numbers in the water and in the sediment. Redundancy discrimination analysis (RDA) showed that the predominant factors influencing the bacteria numbers in the wet and in the dry seasons were different. The bacteria number in the wet season was influenced by all the factors while temperature and ρ(COD_Cr) were the main factors affecting the bacteria number in the dry season.