Abstract: The effects of chloramine dosages and reaction time on the water biological stability were studied by the static test,using assimilable organic carbon (AOC) and microbially available phosphorus (MAP) as evaluation index.The results show that AOC and MAP in the treated water are influenced by chloramine dosage and reaction time.With small varying range of AOC and MAP concentration and slow reaction rate,the change of AOC and MAP concentration were not positively correlated with chloramine dosage,and MAP was less affected by chloramine dosage than AOC.According to the characteristics of the microbial demand for carbon and phosphorus,the influence of chloramine disinfection to MAP should be considered too.