A qualitatively new effects that we discovered in the influence of taxes on investments are discibed. In this Chapter a problem whether it is possible to increase taxing and conserve a good investment climate in the country is studied. Within investment models, developed by Brusov, Filatova, Orekhova earlier (Brusov et al. in Appl Financ Econ 21:815–824, 2011a; Res J Econ Bus ICT 2:16–21, 2011b; Bus ICT (UK) 2:11–15, 2011c; Financ Credit 435: 2–8, 2011d; Appl Financ Econ 22(13):1043–1052, 2012a; J Rev Glob Econ 1:106–111, 2012b; J Rev Glob Econ 2:94–116, 2013; J Rev Glob Econ 2:183–193, 2013b; Cog Econ Financ 2:1–13, 2014a. https://doi.org/10.1080/23322039.2014.946150 ; J Rev Glob Econ 3:175–185, 2014b; Filatova et al. Bull FU 48:68–77, 2008) the influence of tax on profit rate on effectiveness of long-term investment projects at different debt levels is investigated. It is shown, that increase of tax on profit rate from one side leads to decrease of project NPV, but from other side it leads to decrease of sensitivity of NPV with respect to leverage level. At high leverage level L the influence of tax on profit rate increase on effectiveness of investment projects becomes significantly less. We come to conclusion, that taxing could be differentiated depending on debt level of investment projects of the company: for projects with high debt level L it is possible to apply a higher tax on profit rate.