In the last 20 years the average change in BMI among Japanese youth is minimal, but significant changes appear when the categories of overweight/obesity and underweight are investigated within gender. Now intervention programs for Japanese youth on weight management need to be developed. To address the issue, there are a series of steps that could be undertaken utilizing theory of behavior change. Using the Transtheoretical Model-Stages of Change as the health promotion theory an intervention could be developed that would tailor messages to the level of the stage of readiness to weight change that exists among youth. Different aspects of the intervention could be developed and targeted to groups of youth by their needs. To assist with planning and development of the intervention principles of Intervention Mapping could be used to guide development using data from a needs assessment survey to: a) determine youths’ knowledge, attitudes and beliefs about body size, b) determine youth’s barriers to change in body size, c) determine parental knowledge, attitudes and beliefs about body size, d) determine parental barriers to change in youth body size, e) determine the prevalence of health problems from low and high BMI of young females and males, f) determine which youth are at risk-rural/urban areas, socioeconomic status.