Background: Substance dependence has recently turned into one of the most important social problems. Clinical findings have shown personality traits, social relations, attitudes and values, along with emotional intelligence factors such as emotions, feelings, emotions management, challenging with problems, problem solving, tolerating psychological pressure, impulse control, self esteem and interpersonal relations, to affect substance dependence. Consequently, understanding the meaning and developing tools for assessment of emotional intelligence are significantly vital in human psychological health. This study aimed to investigate the relation between emotional intelligence and instable personality in substance abusers. Methods: The present correlational study selected 80 male addicts through available sampling. The subjects referred to the Therapeutic Community Center and Kimia, Yas, and Aban Clinics in Yazd, Iran. Their emotional intelligence and personality were evaluated by BarOn questionnaire and Eysenck personality questionnaire (EPQ) for adults, respectively. Pearson's correlation coefficient was used to assess the correlations between different factors. Findings: There was a negative significant correlation (P = 0.050) between emotional intelligence and instable personality in substance abusers. Problem solving and optimism (P = 0.001), interpersonal relation (P = 0.010), self esteem (P = 0.013), and realities (P = 0.017) had significant effects on instable personality. Conclusion: Based on our findings, emotional intelligence was significantly correlated with instable personality in substance abusers. However, using more accurate tools in order to assess all aspects of personality can give better results. Keywords: Emotional intelligence (EI), Instable personality, Substance abuse.