Abstract: Objective To study the effect of the pre-pregnancy body mass index(BMI) of parents on the risk of neonatal low birth weight, and to provide scientific basis for the prevention of neonatal low birth weight.Methods This was a nested case-control study,based on the Wuhan Birth Cohort Project. The mother-child pairs of pregnant women and their newborns were selected, who entered the/exclusion criteria of case-control and birth weight, there were 61 pairs with the low birth weight newborn(low birth weight group)compared with 534 pairs as the normal birth weight(control group). The basic information of pregnant women and their husbands, and information of maternity check-up and in-patient delivery were collected by questionnaire. Logistic regression model was used to analyze the correlation between pre-pregnancy BMI of pregnant women and their husbands and low birth weight.Results The proportion of low pre-pregnancy BMI pregnant women in low birth weight group was 36.07%, compared with 20.22% in control group; the proportion of normal pre-pregnancy BMI pregnant women in low birth weight group was 57.38%, compared with 73.41% in control group. There were statistically significant differences in low and normal pre-pregnancy BMI pregnant women between the two groups(P<0.05).There were no difference in low and normal BMI of husbands betweenthe two groups(P>0.05).Conclusions Low pre-pregnancy BMI can can significantly increase the risk of neonatal low birth weight, which is one of the high-risk factors of low birth weight.However, pre-pregnancy BMI of husband has no significant effect on neonatal low birth weight. The weight management of pregnant women before and during pregnancy has great clinical significance to reduce the risk of low birth weight.