Introduction: The purpose of the study was to determine the efficacy of motivational interviewing on lifestyle self-efficacy in terms of weight in men. Method: The present research is an experimental study with Pre-test, post-test and a control group that was conducted at different time on 40 subjects suffering from overweight and obesity (Body Mass Index more than 25) working in Isfahan Poly Akril Company in 2009. The subjects were selected by random sampling and were randomly classified into the experimental group (n=20) and the control group (n=20). The intervention consisting of five sessions of group motivational interviewing and weight controlling program was given to the experimental group. The obtained data were analyzed using statistical tests of covariance analysis and dependent t-test, via weight efficacy lifestyle questionnaire. Results: The score of the group receiving motivational interview was significantly higher than the control group in general weight self-efficacy lifestyle scale (p=0.0001) and all its subscales including availability of nutrition (p=0.0001), social pressures (p=0.0001), physical discomfort (p=0.006), negative emotions (p=0.002) and positive entertaining activities (p=0.0001). Conclusion: Including motivational interview in usual weight controlling programs can increase weight self-efficacy lifestyle as a predicting index of losing weight.