Abstract Purpose Examine the annual trends in educational disparity in obesity among U.S. adults aged 18 years and more from 1984 to 2013. Methods Secondary data analysis of 6,147,379 participants in a repeated cross-sectional nationally representative health survey of U.S. adults. Results The obesity prevalence among people with primary school or lower education increased from 17.46% or 3.41 times the prevalence among college graduates (5.12%) in 1984 to 36.16% or 1.73 times the prevalence among college graduates (20.94%) in 2013. In any given year, the obesity prevalence increased monotonically with lower education level. The obesity prevalence across education subgroups without a college degree gradually converged since early 2000s, whereas that between those subgroups and college graduates diverged since late 1980s. Absolute educational disparity in obesity widened by 60.84% to 61.14% during 1984–2013 based on the absolute concentration index and the slope index of inequality, respectively; meanwhile, relative educational disparity narrowed by 52.06% to 52.15% based on the relative index of inequality and the relative concentration index, respectively. The trends in educational disparity in obesity differed substantially by gender, race/ethnicity, age group, and obesity severity. Conclusions There was substantial educational disparity in obesity among U.S. adults and the trend differed across population subgroups.