The methanogenesis of acetamide occurs through a two-step reaction in methanogenic sludges. First, acetamide is hydrolyzed to acetate and ammonia by a strict aerobic bacterium (Bacillus sphaericus), then acetate is used by Bacillus as carbon source or converted to methane by methanogens. In this work, the kinetics of acetamide degradation by B. sphaericus was studied in a continuous reactor with biomass accumulation, fed with acetamide. The oxygen supplied was dissolved in the feed (6.4 mg/L) to resemble conditions in an anaerobic wastewater treatment reactor. A reaction in series model (acetamide --> acetate --> biomass) was used to find the kinetic parameters. Results show that B. sphaericus can hydrolyze acetamide in a second-order reaction with K1 = 1.1 L/g/d, implying that the amount of biomass determines the rate and that no reaction will take place at specific loading rates greater than 35 gAm/gX/d. Growth parameters on acetate, as carbon source, under limiting O2 conditions, are mu(max) = 0.102/d,Ks = 37 mg/L, Y = 0.081 gX/gAm.