Production of industrial enzymes including cellulases requires minimum cost with the downstream processing. The objective of this work was to analyze the precipitation of cellulases by ammonium sulfate in the presence of hydroxypropyl(methylcellulose) as a co-precipitant through the use of statistical experimental design. The model generated with the experimental results showed that high protein recovery can be achieved at high levels of temperature, aging times, and rate of salt-solution addition, and at a low mixing level. The results also allowed the observation that activity recovery was improved at high levels of temperature, rate of salt addition and mixing level, and a low level of aging time.