To investigate the association of both maternal pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) with childhood overweight and adiposity in preschool children. A total of 4 303 preschool children aged 3-5 years were enrolled in our study during June and November 2016 in Guangzhou. Children defined as overweight and obesity were according to the criteria of WHO while weight status during maternal pre-pregnancy was using the China Adult Reference. Gestational weight gain was defined according to the Institute of Medicine guidelines. After adjusting the possible confounding factors, results from the logistic regression analysis showed that both maternal pre-pregnancy overweight and obesity would increase the risk for both childhood overweight and obesity (=1.820, 95: 1.368-2.422). The analysis of covariance results also showed that both maternal overweight and obesity before pregnancy and excessive maternal weight gain during pregnancy increased the BMI -score in children. Maternal GWG over the recommended level were associated with both the childhood overweight and obesity (=1.296, 95: 1.007-1.667). Joint associations of pre-pregnancy BMI and inappropriate GWG were also noticed in the study. Stratified analysis was conducted in three groups according to the pre-pregnancy BMI of the mothers. Result showed that there was no statistical difference in the risks of either overweight or obesity in children (>0.05). However, when compared to mothers with adequate pre-pregnancy higher BMI and adequate GWG, under the combination of high pre-pregnancy BMI and excessive GWG, their adverse effects on childhood overweight and obesity were much higher (=1.574, 95: 1.029-2.409). Both high pre-pregnancy BMI and inappropriate GWG were associated with greater BMI of their offspring. Pregnant women should follow the appropriate weight gain program and help their children to prevent from becoming obese.