The objective of this study was to evaluate the effects of the addition of souari nut peel on the fermentative characteristics and chemical composition of the Mombasa grass silage. A completely randomized design with five levels of addition (0%, 5%, 10%, 15% and 20% in natural matter basis) of souari nut peel with three replicates was applied in the study. The silos were opened at 55 d after starting the ensiling process. The data were analyzed by means of linear/quadratic regression analysis, according to the best fit of the data and the probability values to 5%, using the Statistical Analysis System (SAS, 2002). There were a linear decreasing effect on the neutral detergent fiber (NDF), ash and increasing values for the effluent in the silage. Quadratic effect was observed for crude protein (CP), lignin and pH. For the other factors dry matter (DM), acid detergent fiber (ADF) and gases there was no influence on the addition of souari nut peel. The 15% addition level of souari nut peel increased CP content, decreased NDF and pH, which was recommended to improve the fermentation profile of Mombasa grass silage.