The present study examines the impact of financial and trade liberalization on investment in OPEC member countries. This was descriptive research with a correlational type. The statistical society comprised OPEC member countries. Simple random sampling was used for 14 OPEC member countries. The time interval of 2010-2019 was considered due to heterogeneous published data and consideration of a certain year for all data. The data were derived from World Bank, World Development Indicators (WDI), and Worldwide Governance Indicators (WGI) to be analyzed. Data analysis was done through Eviews software and the generalized method of moments (GMM), and the results indicated the significant impact of trade liberalization on the financial development of selected countries. On the other hand, liberalization affected the financial development of Iran. According to data and statistics, OPEC member countries have relatively poor institutional quality indicators leading to minor impacts of this liberalization compared to other countries with high intuitional quality. It is suggested that the institutional and legal environment of countries be improved in these countries to achieve better and higher impacts of financial and trade liberalization on financial development. تفاصيل المقالة