Using MENA countries data between 1996 and 2017, our papers aim to answer two important questions: the first is: what are the impacts of the financial development and the quality of institutions (or corruption levels) on the informal/shadow economy? and the second question is: how the interaction between the financial development and the quality of institution can affect the informality? Our results show that as the financial system deepens, and the quality of institutions improve as the informal economy gives grounds to the formal one. We also find that the interaction between financial development and corruption level has a positive impact on reducing informality only in the countries with low levels of financial development.