Issues on tax compliance have been extensively studied among researchers since 1960. A review of the tax compliance indicated that there were various factors influencing an individual’s compliance behavior. However, the majority of these studies have focused on the compliance behavior of individual income taxpayers in selected countries. Little is said about the compliance level among business taxpayers especially for small business and partnership. It was reported that, certain small business categories such as restaurants or those who run their business at the roadsides or at hawkers’ centre were found not to fully comply with tax laws. These issues became even more significant for some business taxpayers with the implementation of Self Assessment System (SAS). Under SAS, they are not only required to adhere to tax obligations of doing business, but taxpayers must also have sufficient tax knowledge in order to assess their tax liability correctly and to file tax return forms on time. The tax compliance behavior has been thoroughly explained by the economic deterrence models which primarily emphasize on enforcement and detection variables. These models however have some limitation to fully explain the reasons why many people may or may not comply with tax laws. Since then, many researchers have shifted to focus more on sociology and psychology variables in an attempt to explain taxpayer behavior. Based on this basic model, the objective of this study is to examine suitability of the Theory of Planned and Behavior (TPB) introduced by Ajzen and Fishbein in explaining compliance behavior of sole proprietor taxpayers. These models generally explain how an individual’s attitude towards behavior, subjective norms and perceived behavioral control may influence in making decisions as to whether or not to willingly comply with tax laws. A survey of sole proprietors in Klang Valley would be expected to demonstrate how sole proprietors respond to their tax compliance behavior according to the theory of TPB. The findings of this study is expected to provide insights to Malaysian tax policy makers and the IRBM in understanding the impact of self assessment system on compliance behavior.