This study aims to assess the effectiveness of the WIC program at improving children's dietary quality and to evaluate whether the 2009 food benefit revision further improved the WIC program. A sample of 1,753 children aged between 2 to 4 years from the 2005-2008 and 2011-2016 NHANES was analyzed using a propensity score weighted difference-in-difference approach. Results show that WIC-participating children scored 2.98 points higher (SD: 0.89; P <0.01) in HEI-2015 total scores compared with income-eligible non-participants during 2011-2016. No significant change was observed in the differences of HEI-2015 scores between WIC participants and eligible non-participants from 2005-2008 to 2011-2016.