Obesity and overweight have become increasingly a major public health problem across the world. This study aimed at exploring the effects of motivational interviewing on weight efficacy lifestyle among women with obesity and overweight. A single-blind randomized clinical trial study was conducted on 100 overweight and obese women who attended a nutrition clinic. The samples were selected based on the clinical records and assigned into two groups, namely motivational interviewing arm (50 samples) and nutrition education arm (50 samples). Data were collected using a standard validated questionnaire entitled “weight efficacy lifestyle”. The intervention was designed according to five motivation sessions and four nutrition education programs, such that the participants of the nutrition education arm were also provided with the nutrition pamphlets related to weight control. Data were finally analyzed using the SPSS statistical software by performing the independent t-test, chi-square, LSD and repeated measures ANOVA tests. P<0.05 were considered statistically significant. The mean age of women was 39.9±9.1 and 36.3±8.9 years in the control and motivational interviewing arms, respectively. Compared with the control group, the score of the motivational interviewing group was statistically significant in terms of weight efficacy lifestyle (P=0.0001) and all subscales including social pressure (P=0.0001), physical discomfort (P=0.005), food accessibility (P=0.0001), positive and entertainment activities (P=0.0001), as well as negative emotions (P=0.003). Motivational interviewing appeared to be effective in increasing weight efficacy lifestyle among women with overweight and obesity.