文獻上探討的租稅制度大都採用利潤稅制，然而在實際的經濟體系中，廠商所面對的公司稅制並非利潤稅制。有鑑於此，本文設立一個公司稅制模型，分別在獨占或是寡占市場下，探討稅制的中立性以及廠商的產出與逃漏稅決策。文中發現：與利潤稅制不同的是，不論是在獨占或是寡占市場下，公司稅制均不具中立性；儘管如此，廠商的產出和逃漏稅決策卻仍然具備可分離性。由此可知，稅制的中立性與廠商的產出與逃漏稅決策是否具有可分離性之間並沒有必然的關係。 Most of traditional literatures dealing with corporation tax focus on profit tax. However, in real economy, corporation tax is not equivalent to profit tax. In this paper we provide a corporation tax model and explore its neutrality to firms' production and tax evasion decision, under monopolistic and oligopolistic markets respectively. We found that, different from profit taxes, no matter the market structure is monopoly or oligopoly, corporation tax is non-neutral. Nevertheless, production and tax evasion decision of firms are separable. Therefore, there is no necessary relationship between the characteristics of tax neutrality and production-evasion separability in a tax system.