Tropical pasture production is limited by the supplies of N and even though the application of N fertilizer can be effective in improving pasture productivity, it is an uneconomical practice in most cattle production systems. Therefore, the role of legumes in the improvement of animal productivity and the fertility of acid soils through enhanced nitrogen fixation and nutrient cycling is being studied in Oxisols and Ultisols. Results indicate that legume-based pastures can contribute significantly to improve animal production both in,terms of liveweight gain and milk production. In addition, N, fixing legumes in association with grasses have high potential to improve soil fertility for subsequent crops, most likely due to increased N levels and biological activity of the soils.