SUMMARY
In this paper, we analyze the attitudes of taxpayers regarding tax system. We propose an approach which combines between theory and practice. In the first step, we present a normative approach; based on a theoretical study. In order to produce an empirical knowledge of an aspect of reality we present a descriptive approach; based on a survey of different categories of taxpayers. We have released some conditions of the model of Expected Utility (EU) and we have introduced a new parameter reflecting the efficiency of tax control. Previous studies are based on a maximal efficiency tax control (100%) which is a particular case of our model. We found that for Moroccan case, the fraud is related to the size of companies; it’s more important in the big companies than small and medium enterprises. The findings will help tax authorities to achieve their goals in fighting tax fraud.Keywords: Expected Utility, Prospect Theory, Underground Economy, Tax Fraud, Tax Authority, Tax Audit, Tax Compliance, Taxpayers,JEL Classifications: C5, H3.