Because of efficiency and easiness that it provides, Information Technology (IT) usage has a vital meaning for all sectors. To derive benefits from IT completely, it has to be discovered in all aspects. The purpose of this study is to investigate the reasons behind accountants' IT usage and in this context, compare two social psychology based theories; the Theory of Reasoned Action (TRA) and the Theory of Planned Behavior (TPB). The data, obtained through a questionnaire that was responded to by 437 accountants, shows that if an accountant has a positive attitude and Subjective Norms (SN) towards IT usage, his/her intention towards IT usage is also positive, and the degree of intention is in proportion to the degree of perceived behavioral control. According to the stepwise regression analysis, TPB has higher predictive power than TRA.