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This work analyzed the litter decomposition rates registered in riparian native and reforested forest fragments, to test the hypothesis that the decomposition is dependent on the structural and the floristic composition of the vegetation. The work was carried out in the upper São Francisco River Basin from September 2001 to August 2002. The decomposition rate was measured by quantifying the monthly mass loss of 12 litterbags (20 x 20 cm) containing five grams of dry leaf in each one and located randomly in the two fragments analyzed. Mass loss kinetics was faster in the native forest, reaching the T50% in 5 months (02/2002) while loss in the reforested area was 30% during the same period. This could be reflecting the successional stage characteristic of each fragment and the local climate since the conditions at the native forest (close canopy, less luminosity, higher humidity and cooler constant temperatures) favor the proliferation of microorganisms. This can also be due to differences in floristic composition since the reforested area presents reduced species diversity, with a dominance of Bauhinia variegata L. In addition, the native riparian forest fragment presented higher levels of organic matter content which could contribute to accelerate the litter decomposition rates in this fragment.