Background and Objectives: Obesity is one of major health problems in world. Nowadays, one third of the world suffer from overweight and obesity. Excess body fat accumulation is associated with severe medical and psychological problems. Obesity is a chronic disease that if not treated, causes physical and mental illnesses which ultimately  decreases the ability and capacity to work and makes them more vulnerable against most of disease. The research has been conducted aiming at studying the effects of cognitive behavioral therapy on body mass index and self concept of the overweight people referring to the Health Centers of Ilam province.
 Materials & Methods: A semi-experimental of pre-test, post-test and following up with the control group. Among the eligible male and female volunteers (beingoverweight based on body mass index , not having any severe physical and mental illness, not being pregnant and not being involved in other weight loss programs) , 60 people were selected by using  simple random sampling and they were divided into two groups of experiment (30 people) and control (30 people). The tools of collecting data in this research are: body mass index and Beck Self concept Inventory (BSCI). By using the treatment protocol of Cooper Zefra, the experiment group was treated for 11 months (24 sessions during 44 weeks) including two phases of weight loss and weight maintenance (the phase of weight loss during 30 weeks and the phase of weight maintenance during 14 weeks) in 45-50 minutes sessions, and the control group did not receive any treatment after the sessions, the post test was conducted and data analysis was performed based on multi-variables covariate analysis.
Results: The research results showed that the cognitive behavioral treatment has significantly influenced body mass index and body image perception and self concept of the experimental group.
Conclusion: Cognitive behavioral therapy has an effect, on body mass index and self concept which can be used to control and lose weight.