Background: Opioid agonist treatment, as the most effective treatment for opioid dependency, requires patient adherence for its effectiveness over the long run. Previous studies on psychiatric and non- psychiatric patients indicated that the patient`s temperament has had effect on their treatment compliance. Some studies on different types of addiction have attributed special temperament and character traits to these patients. Introduction: This study aims to investigate the impact of temperament and characteristics on opioid treatment compliance. In this study, the relationship between demographic variables, type of medication therapy, and temperament and characteristics scales of patients against opioid agonists therapy compliance was examined Methods: In this cross-sectional study, 150 patients who had initiated the course of opioid agonist maintenance therapy underwent TCI 125-item test and were followed-up for 2 months regarding compliance. The data were inputted into SPSS 24. K-S and Mann-Whitney U tests were employed to explore the relationship between quantitative and qualitative variables, while for examining the relationship between qualitative variables with each other, Chi-square test was utilized. The significance level in the tests was considered p<0.05. Result: The treatment compliance in this study was 67.2%. In patients who did not have treatment compliance, scores of novelty-seeking (16.7±7versus11.7±4, p<0.001), harm avoidance (16.5±5versus 11.8±5, p<0.0001), reward dependence (12.4±3 versus 10.2±3, p=0.005) and self-transcendence (10.6±2 versus 8.7±2 p=0.002) were higher, but in those who had suitable treatment compliance, scores of persistence (3.5±1 versus 2.3±1, p=0.004) and cooperativeness (17.6±3 versus14.8±4, p=0.004) were higher. Further, some temperament traits were different among patients undergoing treatment with buprenorphine versus methadone (scores of persistence, self-directedness and self-transcendence were higher in the group receiving buprenorphine, while scores of harm avoidance and cooperativeness were higher in the group under methadone treatment). There was also a significant relationship between gender (good compliance: female 100%, male 65%, poor compliance female 0%, male 35%; p=0.04), level of education (higher), as well as type of medication (buprenorphine) and treatment compliance. Conclusion: The results of this study can help to identify high-risk individuals for withdrawing opioid addiction. These people can be a target for pharmacological and non-pharmacological interventions to have their personality traits modified. Investigation of the effect of performing these interventions on treatment compliance can be a subject of future study in this area. Also while there are differences in personality characteristics among cultures, this study investigated Iranian culture more precisely.