The enzyme deactivation in a membrane recycling system for the simultaneous saccharification and fermentation(SSF) was studied under various temperature and pressure. The optimum molecular weight cut off(MWCO) of the ultrafiltration membrane for recycling cellulase and ${eta}$-glucosidase was 50,000. When the cellulase was recycled continuously through the membrane system, it was not deactivated. But the activity of ${eta}$-glucosidase was decreased with an increase in operating temperature and transmembrane pressure. After 720 minutes at $42^{circ}C$ and 24.8 psig , the activity of ${eta}$-glucosidase was reduced by 35% of the initial activity. Such tendencies could be well explained by the results of highly induced shear at the fiber surface of membrane when temperature and transmembrane pressure became higher.