The aim of the present study was to determine the psychometric properties of the Iranian version of the stages of change readiness and treatment eagerness scale, which had been translated and cross-culturally modified into Persian language and back-translated to English. Most specifically, the study sought to validate the Iranian version of the stages of change readiness and treatment eagerness scale, based on the evaluation of two experts. An additional objective was to test the translated instrument for its reliability. For this purpose, the validated instrument was administered to 80 male drug addicts, who were outpatient services at a government rehabilitation center. The results showed the both experts indicated that the items of the translated instrument had very high relevance to their present context. The inter-rater reliability of the scores given by the two experts indicated .805 between the experts' scores for the total scale.The findings showed that the alpha coefficients for the total scale scores at pre-test and post-test were .832 and .787, respectively. Also, the results indicated that the alpha coefficients for all the subscales of the translated instrument at pre-test ranged from .69 to .81. In all the subscales, alphas at post-test ranged from .66 to .79. The Pearson correlation test indicated a high correlation coefficient of .86 between test and retest. In short, the study showed that the translated instrument has very high content validity and high reliability and that it can be used to assess motivation for behavior change and predict treatment outcomes in drug addicts that are receiving treatments in Iran.Keywords: opiate dependency, the stage of change theory, psychometric properties, the stages of change readiness and treatment eagerness scale, Iran