Abstract: In October 2010,an outbreak of bacillary dysentery caused by contaminated water occurred in a school in Qujiang district, Zhejiang province. A total of 178 cases were reported without death. The attack rate was 13.8%. The outbreak affected students in 24 classes. The bacterial detection of source water indicated that total bacterial count, coli group and heat-resistant Escherichia coli indicator were all exceed the limits. Shigella sonnei was detected in 37 of 58 anal swabs collected from the patients, the detection rate was 63.79%.