Background: Childhood obesity is a serious health problem that may affect children until their adulthood. Prevalence of childhood obesity found in Hong Kong has increased significantly. Childhood obesity is believed to be to associate with unhealthy behaviour; therefore, different programs have been conducted previously to promote healthy lifestyle behaviour. So far, the effectiveness of these programs is still controversial. As a parent is an agent having great impact on children, the purpose of the present study was to design a parent-based childhood obesity program, and the effectiveness of this program was assessed.Methods: Design: A randomized, controlled trial, including pre- and post-intervention assessment to examine the effects of a comprehensive intervention program comparing the control condition of a parent’s self-efficacy in managing problem behaviour of children.Subjects: 128 pairs of primary school students and parents in Hong Kong were recruited to participate in a “Healthy for Life” program.Duration: The 20-week program included 10 weeks of intervention and a maintenance period of 10 weeks.Intervention: Participants were randomly divided into an intervention group (n=62) and a control group (n=54). In the intervention group, parents were given education on health knowledge, information on childhood obesity and parenting skills strategies for managing obesity-related problem behaviour of children. In addition, they received a health information sheet nine times during the intervention period. Parents were recommended to use such knowledge and skills to control the body weight of children through modifying children’s unhealthy lifestyle behaviour in the intervention period. In the control group, parents received several health information sheets during the intervention period only.Outcome measures: Parents were asked to complete the “Lifestyle Behaviour Checklist” to assess the problem level and their confidence level in managing the child’s behaviour.