The paper examined the determinants of foreign direct investment inflows in OPEC countries. This paper aims to find out the major determinants of foreign direct investment in the periods 1985 - 2014 using the Generalized Method of Moment (GMM) and panel data. The results show that GDP, exchange rate, imports, FDI in previous periods and gross fixed capital formation have had a positive and significant effect and government size has a negative and significant effect on FDI inflow in OPEC. Also, inflation and economic openness have no significant effect on FDI.