Drug dependency (Addiction) includes a series of physiological, cognitive and behavioral symptoms, and also repetitive model of such symptoms that usually lead to tolerance, withdrawal and obligatory drug consumption behavior. Dependency includes chronic desire to use substance, drug seeking behavior, and unsuccessful attempts to control use of psychoactive substance. There are varieties of behavioral problems (e.g. psychopathic personality disorder, ADHD, conduct disorder, depression with suicide behavior, aggression, insufficient coping styles and attributions) which correlates with substance abuse. Internet addiction (dependency) relate to some kind of behavioral dependency in which people apply that as a defensive mechanism; researchers had borrow drug dependency criteria of DSM-IV-TR to mention its characteristics. As substance dependency, internet addiction is biopsychosocial problems that hold symptoms like tolerance, withdrawal, affective disturbance (depression, irritability) and disruption in social-educational relationships. Once people involve in virtual and unlimited space, neglect their important needs and escape from life demands. Mental occupation and dependency to different database sites like pornographic ones, addiction to computer games, virtual romantic communication, and failing in educational performance as well as family problems may be some of the issues which occur with abusing this technology. This research is a field and applied study; and also a causal-comparative study once considering the control of variables. Statistical universe of the study consist male adults of Tehran with range of 20-30 years old. Sample of the study are 120 adults that selected via non-convenience sampling method (60 adults placed as drug dependence; 60 adults placed as internet dependent). Instruments of the study are MMPI scale (short form-71 items), and GPIUS. Results showed that there is no any significant different between personality characteristics of drug dependent and internet addicted people. Also it was distinguished which there is no significant difference between L, K, Hs, D, Pa, Pt, Sc, and Ma scales of this two groups (i. e., this two groups share in such scales); and there was significant difference only in Hy, Pd, F scales of the two groups.