ObjectiveTo diagnose the subcutaneous tumors in the NIH mice in bred in the laboratory animal center in our company.MethodsTo statistically analyze the morbidity, body weight and parturition times of the NIH mice bred in our animal center. Tumor samples were taken for pathological examination. ResultsOne hundred and fifty-four subcutaneous tumors were found among 11711 mice. The pathological diagnosis of the subcutaneous tumors was fibroadenoma, and the incidence rate was 1.32%. ConclusionsThe tumor of NIH mice bred in our company laboratory animal center is fibroadenoma. The etiology of this tumor needs to be further investigated.