We investigated the aerobic and anaerobic biotransformation of atrazine using laboratory -scale batch reactors containing wetland water and sediment. After 38 weeks of anaerobic incubation, atrazine in the water phase dropped from the initial 10 ㎎/L to 4.2㎎/L. In contrast to the aerobic biotransformation, a significant level of hydroxyatrazine was detected in the sample reactors during 38 weeks of anaerobic incubation. Furthermore, a trace amount of a possible deethylhydroxyatrazine was detected in the anaerobic BSM sample reactor. However, none of the dealkylated metabolites were observed. In contrast to the anaerobic condition, atrazine disappeared rather rapidly within 21 days of incubation after 42 days of stationary phase under aerobic conditions. BSM increased the atrazine biotransformation rate under anaerobic conditions, but decreased the rate under aerobic conditions.