AbstractA dissolving pulp of low cellulose viscosity represents a pulp of high quality; hence, it is often necessary to decrease the initial dissolving pulp viscosity. One so-called environmentally friendly approach to further reducing the dissolving pulp viscosity is to treat the dissolving pulp with cellulase enzymes. In this study, the kinetics of the decrease in cellulose viscosity during a cellulase treatment was investigated. The study showed that the kinetics of the cellulose degradation during a cellulase treatment can be divided into at least two phases, where the initial phase is very fast and the final phase is very slow. The kinetic two-phase model for the viscosity degradation that has been developed in this project can be used to predict and control the final pulp viscosity of dissolving pulps.