No large population-based study has focused on both maternal paternal risk factors for low birthweight (LBW) in China. We aimed to identify parental risk factors associated with LBW. A population-based, retrospective cohort study was conducted on 202,725 singleton infants at 37-42 weeks. These term singleton newborns were classified as LBW with birthweight < /=2500 g(TLBW) and normal birthweight between 50(th) to 97(th) percentile (TNBW 50(th)-97(th)) according to Chinese singleton norms. Multiple logistic regression analyses were used to find those parental risk factors of LBW by comparing two groups. TLBW and TNBW(50(th)-97(th)) occupied 4.8% and 70.8% of the study population, respectively. Logistic regression showed a significant association with positive maternal hepatitis B surface antigen (RR = 1.979, P = 0.047), irregular folic acid intake (RR = 1.152, P = 0.003), paternal history of varicocele (RR = 2.404, P = 0.003) and female babies (RR = 1.072, P = 0.046). Maternal smoking, hypertension and history of stillbirth were found related to LBW but no statistically significant. Positive maternal hepatitis B surface antigen, irregular folic acid intake, paternal history of varicocele had a negative effect on birth weight. Measures are necessarily taken to avoid them to improve pregnancy outcomes. Further studies should be done to investigate each detailed risk factors on LBW.