Abstract: ObjectiveTo analyze the epidemiological features and risk factors of the hepatitis A outbreak in a school in Ninghai County. MethodsField survey, individual survey and case control study were conducted. ResultsThirty two cases occurred with the attack rate of 6.93%, and 59 cases of latent infection were detected with the infection rate of 12.77%. Case control study indicated that drinking the water from the well beside teachers canteen was main risk factor to cause this outbreak. ConclusionSince the contaminating of well water was main risk factor to cause the hepatitis A outbreak, it is necessary to strengthen the management of drinking water to prevent such outbreak.