A main objective of the regional integration in West African Economic and Monetary Union (WAEMU) is the effective harmonization of national legislations at Community level notably tax legislation. To coordinate taxation in the zone, WAEMU Commission translates into Directives the Decisions taken by the Council of Ministers of the member states. The implementation of the Community acts by countries through tax reforms may impact on their revenue performance. This paper evaluates the impact of the Directives both in terms of coordination and revenue mobilization. It relies on a comparative case study using the synthetic control method developed by Abadie and Gardeazabal (2003) and extended by Abadie, Diamond, and Hainmueller (2010 & 2015). The main results are that the tax coordination affected the revenue mobilization in the Union but the impact is different across countries.