Taxation due to its mandatorily and regularity is the most important source of government revenue in financing development programs, including strengthening physical infrastructure. Accordingly, the issue of identifying the determinants of tax revenue is of particular importance in any economy that Iran's economy cannot excluded from this principle. Thus, this study investigates the effect of macroeconomic variables (economic growth, inflation, exchange rate and Openness) on government tax revenues using an Autoregressive Distributed Lag (ARDL) model in Iran during 1978-2018. The results from this study support the views of Calder (1962), Tudaro (1969), Olivera-Tanzi (1977), and Tanzi (1989) and show that economic growth, inflation, official exchange rate changes, and urbanization-Due to the underdevelopment of the Iran's economy-have a negative impact on tax revenue. Also, our findings indicate that Openness and share of services in GDP have a positive and significant effect and financial instability has a negative and significant effect on tax revenue. Finally, based on the findings of this study, there is no evidence that the variables of exchange rate fluctuations, government oil revenues and share of agricultural and industrial in GDP, have a significant impact on tax revenue.