The primary human source of N2O is agricultural soil management. Fertilized soils may affect N2O emission in several ways. Our aim was to evaluate the N2O emission potential of tropical soils after the application of locally-produced exogenous organic matter (EOM) in Madagascar and Reunion Island. 34 EOM including agricultural, agroindustrial and urban effluents were used. The denitrifying enzyme activity (DEA) test was carried out through incubations of soil-EOM mixtures using or not acetylene. As results, for the Reunion andic soil, DEA ranged of 0.39 to 0.89 ?gN2O-N.h-1.g-1 dry soil depending on the EOM applied to the soil. Activities ranging between 0.70 and 1.53 ?gN2O-N.h-1.g-1 dry soil were measured for Malagasy mixtures. In general, ratio N2O/(N2O+N2) value varied between 0.83 and 1.29. A first appreciation of the environmental impact of applying EOM in two common types of soils in the Indian Ocean area was achieved in this study.