Tax evasion and tax avoidance, in Tanzania, has been a serious problem even before the introduction of Tanzania revenue Authority. The objective of this study was to investigate on the causes of tax evasion and tax avoidance in Magu district. The study used logit model for regression analysis, because the dependent variable was a dummy. The findings revealed that higher level of education and higher levels of income lead to low levels of tax evasion and avoidance while higher tax rates lead to higher levels of tax evasion. The study recommends that in order for the Tanzanian government to control tax evasion and avoidance, it must increase the people’s incomes and educate more people. Tax rates should be reduced if cases of tax evasion have to be reduced.