OBJECTIVE:To investigate the occurance of diaper rash and thrush of newborns who were treated with β-lactam antibiotics. METHODS:79 newborns were treated intraveneously with β-lactam antibiotics and the controls were 80 healthy newborns. The incidences of the above two groups of diaper rash or thrush were compared, and the effects of some related factors were analysed. RESULTS: The incidence of suprainfection in the antibiotic group was higher than that of the control group. The higher incidence of the diaper rash in the patient with strong antibiotics, the longer treatment period or lighter baby's body weight. Thrush was found in premature babies or lighter body weight ones. There was no relationship between the two side-effects and the baby's sex or primary diseases. Thrush was not related to the duration of the treatment.CONCLUSION:The newborns especially premature babies, lighter body weight ones or to be treated for a long period, must be taken care of to prevent diaper rash or thrush.