Objective To investigate the association between different levels of birth weight and the risk of overweight and obesity in children aged 3 years and under. Methods Between 2009 and 2011, health care records of 55,925 children had been collected, and body weight and length had been measured from birth to 3 years old. Results Prevalence of overweight/obesity (BMI ≥85th percentiles and BMI ≥95th percentiles, referring to WHO BMI standards) at 0.5, 1, 2, and 3 years of age are 34.7%/16.8%, 36.4%/17.7%, 26.6%/11.0%, 22.3%/9.3%, respectively. There was a positive association between birth weight and childhood overweight or obesity from 6 months to 3 years of age. After adjustment for gestational age, maternal age, weight gain during pregnancy, maternal history of diabetes, mother's and father's education, occupation, and health status, family income, feeding modalities, and sex, the odds ratios (ORs) of overweight or obesity were significantly higher among children whose birth weights were 3,000–3,499 g (1.35–1.53 folds), 3,500–3,999 g (2.09–2.37 folds), 4,000–4,499 g (2.80–3.32 folds), and more than 4,500 g (3.54–4.90 folds), compared with the reference group (2,500–2,999 g). Conclusions Higher levels of birth weight were associated with an increased risk of overweight or obesity among Chinese children from 6 months to 3 years of age. Am. J. Hum. Biol. 26:331–336, 2014. © 2014 Wiley Periodicals, Inc.