In the past few decades, municipal amalgamations have become a prevalent way for local governments around the world to exploit economies of scale.While most empirical research about municipal merger has focused on efficiency of local public goods provision, it is rare in the literature to explore how merger promote economic growth in a developing country context.This research investigates the policy experiment of city-county merger in China between 2000 and 2004 and identifies its effects on local economic agglomeration.Based on a comprehensive urban dataset that covers all Chinese prefecture-level cities before and after merger, we found that merger significantly increased local GDP level and GDP density; moreover, the effects are stronger in cities with higher market access.In general, the evidence of municipal merger in China is supportive of urban agglomeration economies.