This study aimed to examine the association of late bedtime and fast eating speed, both individually and interactively, in predicting overweight and obesity in Chinese preschool-aged children. This was a cross-sectional survey among children aged 3-6 years. Overweight and obesity is defined according to the WHO, IOTF, and China criteria, respectively. Total 1123 preschool-aged children were analyzed. After multivariable adjustment, late bedtime after 11:00 pm and fast eating speed increased the risk of overweight and obesity significantly under the WHO (odds ratio [OR]=1.92 and 1.37, 95% confidence interval [CI]: 1.31-2.80 and 1.00-1.88), IOTF (OR=1.47 and 1.46; 95% CI: 1.00-2.15 and 1.07-2.00), and China (OR=1.66 and 1.39; 95% CI: 1.20-2.29 and 1.07-1.80) criteria. Relative to bedtime before 11:00 pm and eating speed >= 30 min, there was a graded increase with presence of either bedtime after 11:00 pm or eating speed 15-30 min and <15 min. Particularly, the presence of both bedtime after 11:00 and eating speed <15 min yielded the largest OR under the WHO (adjusted OR, 95% CI: 3.98, 1.27-12.51), IOTF (3.59, 1.12-11.50), and China (4.84, 1.71-13.69) criteria. Taken together, our findings indicate a synergistic interaction between bedtime and eating speed in predicting overweight and obesity in Chinese preschool-aged children.