Abstract: In this study, the effects of the Customs Union on the foreign trade between European Union and Turkey were analyzed using 1980-2015 period data. According to the co-integration test results of the export and import models, CU positively affects both Turkey's exports to the EU and its imports from EU. The overall results of the study show that the CU has trade creation effect; however this effect is very limited. Examination of the market share of Turkey's total exports after joining the CU shows that the decrease of EU's share and the increase of the exports to third country markets is an indicator of the fact that CU is not a trade diversion effect for Turkey. Keywords: Economic Integrations, Customs Union, European Union, Turkey, Foreign Trade.