Objective To study the incidence of lactase deficiency and the risk factors affecting intestinal lactase secretion in newborns with lactase deficiency.Method From February to December 2016,newborns admitted to the neonatal ward of the Affiliated Hospital of Hangzhou Normal University were enrolled in this prospective study.Urine samples were taken within one to two hours after feeding for galactose qualitative tests,and the related clinical data were recorded.The newborns were assigned into lactase deficient group and non-lactase deficient group according to the test results.Then the risk factors of lactase deficiency were analyzed comparing the clinical data between the two groups.Result A total of 1 022 newborns were hospitalized during the research period,of whom 213 were enrolled in this study according to the inclusion criteria.154 cases had positive results in the urine galactose qualitative tests,yielding the incidence of lactase deficiency of 72.3 ％.42 cases had lactose intolerance symptoms,and the incidence of lactose intolerance was 27.3 ％ (42/154).Age and positive family history in lactase deficient group were higher than non-lactase deficient group (10.3 ±6.4 d vs.8.1 ±5.8 d and 23.4％ vs.10.2％),while the gestational age of lactase deficient group was lower than non-lactase deficient group (37.8 ±2.9 weeks vs.39.0 ± 1.7 weeks),and the differences between the two groups were statistically significant (P ＜ 0.05).No significant differences existed in gender,birth weight,antibiotics use and feeding volumes between the two groups (P ＞ 0.05).Multivariate Logistic regression analysis showed that age (OR =1.065,95％CI 1.007 ～ 1.127) and positive family history (OR =2.912,95％ CI 1.053 ～ 8.056) were the risk factors of lactase deficiency.Gestational age (OR =0.747,95％ CI 0.617 ～ 0.904) was the protective factor of lactase deficiency in newborns.Conclusion The incidence of lactase deficiency in newborns is high,but not all the newborns manifest lactose intolerance symptoms.Age and positive family history were the risk factors while gestational age was the protective factor for lactase deficiency in newborns.