On 13 June 2013, a fever and diarrhoea outbreak occurred in a boarding school in Sichuan Province. We conducted a field investigation and compared food exposure of 81 case students and 104 control students (years 7 and 8) in order to identify the source of infection. There were 401 cases identified (399 students and two cooks). The attack rates were 23–46% in nursery, primary, and secondary schools, but 0% in the high school. Eighty-five percent of case students, consumed cowpea salad compared to 60% of control students at lunch on 12 June (odds ratio 3·1, 95% confidence interval 1·3–7·8). The cowpeas were stored at room temperature for 3 h in a bucket previously used to store raw ingredients. The bucket was cleaned using water without a disinfectant. There were two buckets of cowpea, one for the high-school students and another for the other students. This Salmonella outbreak was likely caused by the cowpea salad due to cross-contamination via a storage bucket.