This paper investigated the correlation between maternal employment and childhood obesity, and the probable mechanisms for that correlation. Previous papers have found that a child is more likely to be overweight if his/her mother worked more hours per week over the child‟s life, but few have looked into the mechanisms that caused the higher likelihood. Brown et al. (2010) and Chia et al. (2008) investigated the probable mechanisms, but their data have limited measures of children‟s lifestyle variables. The data used in this study have nine measurements of activities and seven measurements of diet; which is more inclusive than that of Chia (2008) and Brown et al. (2010)‟s. Additionally, my methods included an adjustment explicitly modeling the endogeneity of mother‟s employment. The model in this paper followed the model in Anderson et al. (2003) in which energy expenditure and caloric intake enter linearly into the weight, and energy expenditure and caloric intake were determined by maternal employment, and mother, family and children‟s characteristics. Then, this research paralleled Chia (2008)‟s models that extended the Anderson et al. (2003) model and looked into the relationship between maternal full-time employment and energy expenditure and caloric intake, captured by children‟s diet and activities. Using Early Childhood Longitudinal Study, Kindergarten data that has children‟s activities and diet information, and selection-corrected ordered probit to account for endogeneity issues that may influence both maternal full-time employment status and the variables of interest (overweight status, diet and energy expenditure), this paper found that the relationship between mother‟s fulltime status and the child‟s overweight status is positive (19 percentage point marginal effect). Maternal full-time employment status affects child‟s overweight status through affecting the child‟s habit in watching TV and in diet, such as the number of times the child drank juice and ate vegetables. If the endogeneity issue is ignored, the marginal effect of maternal full-time employment is biased toward zero.