Objective To explore the occurrence of overweight and obesity in preschoolers and their immediate relatives (parents, grandparents and maternal grandparents), as well as the relationship between them, so as to provide scientific basis for preventing and reducing overweight and obesity in preschoolers. Methods A stratified random cluster sampling method was adopted to select 2 217 preschoolers in Yuhua district of Nanjing from May to June in 2019.The information of children, such as age, gender, birth weight and the anthropometric data of their immediate family members were collected by questionnaire survey.The anthropometric indexes of children were measured by standard way in kindergarten.The relationship between overweight and obesity in preschoolers and their immediate relatives was analyzed. Results The rates of overweight and obesity in preschoolers were 7.80% and 2.75%, respectively.The incidence of obesity in boys was significantly higher than that of girls (3.4% vs.2.0%, P＜0.05).In the middle-aged parental generation, the prevalence of overweight and obesity was 36.1% and 11.1% in men, respectively, both significantly higher than those in women (13.6%, 3.3%) (P<0.001).Whereas in the grandparental generation, the prevalence of obesity was significantly higher in women than that in men (grandparents:10.1% vs.5.9%, P<0.001; maternal grandparents:7.5% vs.6.2%, P<0.05).According to the ordered Logistic regression model, it was found that maternal overweight(OR=1.614, 95%CI:1.132-2.301, P＜0.01) and paternal obesity (OR=2.584, 95%CI:1.773-3.765, P＜0.001) were independent risk factors for childhood overweight and obesity.Obesity of grandparents and maternal grandparents had no significant relationship with childhood obesity. Conclusions The prevalence of overweight and obesity in middle-aged men is highest among three generations.Parents' overweight or obesity could significantly increase the risk of obesity in preschoolers.