Background: The 'Healthy Dads, Healthy Kids' program was designed to help overweight fathers lose weight and positively influence the health behaviors of their children. The aim of the current study was to evaluate the previously established program in a community setting, in a large effectiveness trial. Methods/Design: The Healthy Dads, Healthy Kids community trial consists of three stages: (i) Stage 1 - program refinement and resource development (ii) Stage 2 - community randomized controlled trial (iii) Stage 3 - community effectiveness trial. The program will be evaluated in five Local Government Areas in the Hunter Valley Region of NSW, Australia. For the community randomized controlled trial, 50 overweight/obese men (aged 18-65 years) from one Local Government Area with a child aged between 5-12 years of age will be recruited. Families will be randomized to either the program or a 6-month wait-list control group. Fathers and their children will be assessed at baseline, post-intervention (3-months) and 6-months. Inclusion criteria are: body mass index 25-40 kg/m2; no participation in other weight loss programs during the study; pass a health-screening questionnaire; and access to a computer with Internet facilities. In the community trial, the program will be evaluated using a non-randomized, prospective design in five Local Government Areas. The exclusion criteria is body mass index < 25 kg/m2 or lack of doctor's approval. Measures will be collected at baseline, 3-, 6- and 12-months. The program involves fathers attending seven face-to-face group sessions (three with children) over 3-months. Measures: The primary outcome is fathers' weight. Secondary outcomes for both fathers and children include: waist circumference, blood pressure, resting heart rate, physical activity, sedentary behaviors and dietary intake. Father-only measures include portion size, alcohol consumption, parenting for physical activity and nutrition and parental engagement. Process evaluation will determine the fidelity, dose (delivered and received), reach, recruitment and context of the program. Discussion: As a unique approach to reducing obesity prevalence in men and improving lifestyle behaviours in children, our findings will provide important evidence relating to the translation of Healthy Dads, Healthy Kids, which will enable it to be delivered on a larger scale.