The time profile of an enzymatic reaction at an early stage is generally considered to be linear. We observed that the time profile of the hydrolysis of 1 mM p -nitrophenyl-β-D-glucoside (pNP-Glc) by a β-glucosidase obtained from Agrobacterium tumefaciens (Cbg1) was not linear before 5% of the substrate was consumed, even though the initial concentration of the substrate was much higher than its K m value. The time profiles obtained with higher concentrations of pNP-Glc suggested that the time profile was the function of the absolute concentration of p -nitrophenol (pNP). The addition of various alcohols made the time profile linear. A self-transferring product inhibition model was constructed in which the pNP generated during the hydrolysis acts as an acceptor substrate to inhibit the hydrolysis. The theoretical curve agreed well with the experimental data.