Objective To analyze the causes and suspicious risk factors of an outbreak of foodborne diseases involving several kindergartens in Ji'nan City, so as to provide basis for strengthening the prevention and control of foodborne diseases in schools. Methods Field epidemiological method was used to investigate the cases, descriptive epidemiological method and cohort study method were used to analyze the data and factors of the outbreak. Results A total of 195 children from 11 kindergartens in four districts of Jinan City were involved. The incidence rate was 17.06%. The age range was 3~6 years old. The ratio of male to female was 1.41∶1 (114/81), no staff got sick. The result of cohort study showed that drinking XX brand pasteurized milk increased the risk of disease by 17.06% (RD=17.06,95% CI:15.01,19.11). Further statistical analysis showed that the rate difference (RD) value of drinking XX brand pasteurized milk on August 9 was 2.82%-35.44%, which was statistically significant, suggesting that drinking XX brand pasteurized milk increased the risk of disease by 2.82%-35.44%. Bacillus cereus was detected in 13 vomit samples and 8 pasteurized milk samples from kindergartens, and the count of Bacillus cereus in 8 milk samples was more than 10⁵ CFU/g, which confirmed that XX pasteurized milk was contaminated by Bacillus cereus. Conclusion The outbreak of foodborne diseases was caused by pasteurized milk contaminated by Bacillus cereus. It is necessary to further strengthen food safety supervision and foodborne disease monitoring in schools, and actively carry out health education to effectively prevent the occurrence of such events.