One of important factors in economic growth and development is tax. Incomes are the basis of tax calculation; and, based on the agency issue, managers have sufficient motivations to manipulate incomes. Manipulation of incomes can affect tax rates and tax evasion/ avoidance levels, on the other hand. On this basis, the main objective of present research is to investigate relationships between income manipulation and effective tax rates within companies listed on Tehran Securities Exchange. In this direction, relationships of variables of income smoothing and optional accrual items with effective tax rates are examined. Research statistical sample includes 113 companies listed during the period of 2010-2016. Findings of simple regression cross-sectionally and collectively indicate that, as 2 measures of income manipulation, income smoothing and optional accrual items have significantly positive relationships with effective tax rates.