Risk management is one of the instruments for tax compliance management which are aimed to improve taxpayers' compliance. In this view, effective factors of taxpayers risk are identified, meanwhile taxpayers are classified into different levels and effective tax strategies which are coordinated with each level of risks are chosen and utilized in order to institutionalize rendering services and suitable education, self-assessment and voluntary compliance. The size of taxpayers is considered to be one of the main factors affecting their risks. Indeed, developing and implementing effective and targeted strategies for tax compliance regardless of taxpayers' size will not be possible. In this research, the independent variable, the taxpayers' size, and its significance relationship to the dependent variable, the risk of taxpayer compliance, were tested in two forms which were distributed among 210 legal taxpayers of the Western Tehran Tax affairs general directorate. In order to test the significance relationship of the taxpayers' size variable, the Kruskal- Wallas non-parametric one-way variance was used. At the end, the test showed that the taxpayers' size variable bore an inverse significant relationship to the dependent variable, the risk running by taxpayer. Furthermore the inverse relationship between taxpayers' size and the risk running by corporate operating in different manufacturing, service, trading, and contracting sectors have also been examined. In this regard, we witnessed an inverse significant relationship between taxpayers' size and the risk of compliance simply for the taxpayers operating in trading sector. In other words, the risk of their compliance would diminish as the size of the taxpayers operating in the trading sector grows.