This article aims at to verify the effects of the trade agreements implanted in the textile sector (Multi-fibre Agreement, Agreement on Textiles and Clothing and liberalization of the textile sector in the world trade) about the integration among the internal and external prices of the cotton of january of 1990 to february of 2009. For that, they were employees the tests for unitary root and Johansen’s co-integration; estimation and analysis of and the vector error correction model (VEC) and the exogenicity test. The results revealed that the markets brazilian and american can be considered integrated in all of the analyzed samples, indicating that variations of price of the cotton happened at a market is reviewed to the other market in the long period, however that transmission is not accomplished in a complete way, because the hypothesis of perfect integration between these markets was rejected in all of the studied situations, invalidating, therefore, the Law of One Price.