Background: Schools are important venues for providing and promoting physical activity, but little is known about how school websites are being used for these purposes. Completing a content analysis of existing school websites is essential to understanding their function and value relative to supporting physical education (PE) and physical activity. Methods: We conducted a quantitative, cross-sectional, systematic content analysis to analyze and identify correlates of the website features of 990 private elementary schools located in 325 California cities/localities. Results: Nearly all schools (98%) had a functioning website, but PE and physical activity content were displayed sparsely and inconspicuously. Regression models identified 10 predictors of website PE/physical activity content, including religious affiliation and having a separate webpage for PE. Conclusions: Websites can serve many functions, including providing information on the school vision/goals, curriculum content, class schedules, extracurricular activities, and core topics. This study is among the first to carry out a systematic analysis of school websites relative to PE and physical activity. Schools did not use the full potential of their websites to inform constituents about physical activity or to promote it. Schools should scrutinize their websites to ensure content and messaging are consistent with enabling students to engage in sufficient health-promoting physical activity.