This study compared the self-reported physical activity, perceived social support for, and perceived barriers to, physical activity of primary and secondary school children from Hong Kong and Australia. Hong Kong boys and girls reported spending significantly less time, outside of school hours, on physical activity than their Australian contemporaries (p less than 0.05). There was significantly higher perceived support for activity from Australian parents (p less than 0.001), teachers (p less than 0.001) and peers (p less than 0.001) compared to their Hong Kong counterparts. Parental support significantly correlated with self-reported activity in Australia, but not in Hong Kong. These data add support to the notion that strategies to increase physical activity need to embed family and school. (Contains 5 tables and 1 figure.)