Within investment models, developed by Brusov, Filatova, Orekhova earlier (Brusov and Filatova, Financ Credit 435:2–8, 2011; Brusov et al., Appl Financ Econ 21(11):815–824, 2011; Brusov et al., Res J Econ Bus ICT 2:16–21, 2011; Brusov et al., Res J Econ Bus ICT 2:11–15, 2011; Brusov et al., Appl Financ Econ 22(13):1043–1052, 2012; Brusov et al., J Rev Glob Econ 1:106–111, 2012; Brusov et al., J Rev Glob Econ 2:94–116, 2013; Brusov et al., J Rev Glob Econ 2:183–193, 2013; Brusov et al., Cogent Econ Financ 2:1–13, 2014; Brusov et al., J Rev Glob Econ 3:175–185, 2014; 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.