Increasing interests have been shown in associations between socioeconomic status (SES) and obesity in relation to health inequality. The research objectives were 1) to examine associations between SES and child obesity (including overweight) in Korea over 10 years and 2) to explore possible underlying mechanisms of relationships between SES and obesity. This study used the nationally representative data (KNHA-NES) from 1998, 2005, to 2009. Children (10-18 year-old) were grouped by household income (low, middle-low, middle-high and high) adjusted for the number of family members. Z-scores of height, weight, and BMI for each child were calculated from measured anthropometric data using the 2007 Korean national growth charts. No statistically significant associations were found, however, changes in association patterns were noted. The lower SES group showed shorter height as well as lighter weight among Korean children. More research should be conducted to understand the effects of socioeconomic status on child obesity.