This paper builds a structural bargaining model to assess whether the signing of NAFTA led to deeper trade liberalization in the WTO negotiation (Uruguay Round). In the first stage of the model, NAFTA members negotiate the preferential tariffs; and in the second stage WTO members negotiate the MFN (most-favored nation) tariffs. I estimate the trade and the bargaining parameters to match the trade flows in 1995 and the negotiation outcomes of both NAFTA and the Uruguay Round. Then I use the estimated model to simulate a counterfactual outcome where the Uruguay Round proceeds without the signing of NAFTA. The results show that the average tariffs in the Uruguay Round would have been 0.92 percentage points higher in the absence of NAFTA and that both NAFTA countries and the world experience welfare loss. The finding supports the view that preferential trade agreements are building blocks to the WTO negotiation.