Objectives: The aim of the present study was to examine the sensitivity level of Behavioral Approach System (BAS) and Behavioral Inhibition System (BIS) as probable predisposing factors for substance abuse. To this end, the difference of sensitivity levels of BAS and BIS were assessed in substance abusers, cigarette smokers, and normal individuals. Method: The present causal-comparative study compared the sensitivity levels of approach and inhibition behavioral systems in the following three groups: substance abusers (n=43), cigarette smokers (n=45) and normal individuals (n=55), using BIS/BAS scales. Data were analyzed using c² distribution, one way analysis of variance, multivariate analysis of variance, and follow-up tests. Results: The scores of BAS subscale in substance abusers and cigarette smokers were higher than that of normal individuals (p≥0.05), but there was no difference in this regard between substance abusers and smokers. In the BIS subscale, the cigarette smokers scored higher than the other two groups (p≥0.05). Conclusion: Substance abusers and smokers have a more sensitive BAS than normal individuals, which predisposes them to appetitive behaviors. These findings are in line with the Reinforcement Sensitivity Theory, which predicts a relation between BAS, appetitive behaviors and substance abuse.