ObjectivesChildren in China have low levels of physical activity. We developed a school-based behaviour change intervention to increase their physical activity levels. The study aimed to determine the feasibility of undertaking a cluster randomised controlled trial (RCT) in the future. This future cluster RCT will evaluate the effectiveness of the intervention.DesignFeasibility cluster non-RCT design.SettingTwo public schools (one intervention and one control) in Yangzhou, China.ParticipantsChildren aged 10–12 years and their parents.InterventionThe 16-week school-based behaviour change intervention to increase physical activity levels consisted of three components (a) health education (physical education), (b) family involvement and (c) school environment support.Outcomes measuresWe estimated important parameters that are needed to design the future cluster RCT, such as SD of the primary outcome (ie, 7-day steps in children), intracluster correlation coefficient (ICC), recruitment of child–parent dyads, follow-up of children, completion of and time needed for data collection among children and intervention attendance.ResultsSixty-four children and their parents participated in the study (32 per study group). The SD of the primary outcome was 34 519 steps. The ICC was 0.03. The recruitment and follow-up rates were 100%. The completion of data collection was 100% (except for the 7-day steps at baseline—one child lost the step log in the intervention group and two children lost their pedometer in the control group). The time needed to complete the self-reported questionnaire by children was around 15 min per study group, and the measurement of their anthropometric parameters took around 40 min per study group. The intervention attendance was 100%.ConclusionsBased on the promising recruitment, follow-up, completion of and time needed for data collection and intervention attendance, it would be feasible to undertake the future cluster RCT in China.Trial registration numberChiCTR1900026865.