Objectives. We sought to determine the extent to which child care centers in South Carolina improved physical activity practices after a new policy took effect. Methods. In 2012, South Carolina adopted new mandatory physical activity standards within its child care quality enhancement program. This quasi-experimental study used North Carolina, a state not making policy changes, as the comparison. Participants were 34 child care centers in South Carolina and 30 centers in North Carolina. Researchers used the Environment and Policy Assessment and Observation (EPAO) tool to conduct center observations before and after policy implementation and then conducted repeated-measures linear regression with interaction between state and time for the Physical Activity Environment Total Score and the 8 subscale scores. Results. Compared with centers in North Carolina, EPAO subscale scores in South Carolina centers increased significantly for the Fixed Play Environment (P .001) and Physical Activity Training and Education (P = .015). The state-by-time interaction of Physical Activity Environment Total Score approached statistical significance (P = .06). Conclusions. Adoption of new physical activity standards in South Carolina child care centers was associated with improvements in practices aimed at increasing children's physical activity. (author abstract)