Hemicellulase binding onto wood fiber was investigated in a turbulent mixing environment created by an axial flow impeller. The binding of the enzyme was found to be a function of the intensity of agitation, reaction time, and type of pulp. Enzyme binding to bleached softwood pulp increased with time initially, reaching a maximum after 5 min of mixing. Binding of enzyme onto unbleached softwood pulp decreased with time and with increasing shear rate. It appeared that the higher the shear rate, the lower was the binding of hemicellulase. The binding of enzyme to unbleached pulp was found to be lower than the binding to bleached pulp. A lignin interference with the protein assay was observed when soluble lignin degradation products from unbleached softwood pulp were leached into the bulk solution. The leaching was found to be mainly a function of time, temperature, and pH. The rate of soluble lignin release was high in the early stages of mixing, but decreased with time. The activity of hemicellulase decreased with increased shear rate and with mixing time. Hemicellulase was resistant to deactivation at a low shear rate, but a higher shear rate deactivated the enzyme almost completely after 30 min.