An experiment was conducted to evaluate the effect of three application rates (0, 1 and 2 times the recommended rate) of a commercial additive containing a lactic acid-producing bacterial inoculant as well as plant cell walldegrading enzymes, on the microbial succession, fermentation end-products, and aerobic stability of guinea grass (Panicum maximum var. Jacq.) silage. Vegetative material was harvested at 30% dry matter (DM) and chopped into 2.5-cm pieces. At ensiling, three treatments were imposed: no additive (control), additive applied at recommended rate, and at 2x the recommended rate. Three silos per treatment were opened after 0, 2, 4, 7, 14, 28, and 56 d of fermentation, and siiage was analyzed for pH, microbial succession, chemical composition, fermentation end-products and aerobic stability. For aerobic stability determination, three silos per treatment were opened at the end of the fermentation period, and silage (400 g) was exposed to air for three days in Styrofoam containers lined with plastic. After 0, 1, and 3 d of aerobic exposure, silage was analyzed for pH, microbial populations (total bacteria, yeast and molds), water soluble carbohydrate content, fermentation end-products and in vitro dry matter degradability (IVDMD). Temperature was monitored daily and dry matter recovery (DMR) was calculated after 1 and 3 d of aerobic exposure. The addition of the commercial additive, applied one or two times the recommended rate, increased (P < 0.05) the lactic acid producing bacterial population and decreased (P < 0.05) conforms during early stages of the fermentation process, but did not influence the yeast and mold populations or the chemical composition of the resulting silage. Use of the inoculant-enzyme mixture also resulted in siiage with higher lactic acid content 56 days post ensiling. The silage additive did not inffuence pH, temperature, microbial populations, soluble carbohydrate content, IVDMD or DMR of guinea grass silage after exposure to air. In summary, use of the commercial additive applied at the recommended rate partially improved the fermentation characteristics of guinea grass silage, but did not enhance its aerobic stability. Increasing the application rate to twice the recommended rate did not result in better fermentation.