Rhamnolipid biosurfactant. as an addition to rice straw hydrolysis bioprocess, could not only stimulate the hydrolysis rate, but also reduce the requirement for large amount of cellulases and promote its recycling process. In this article, through the observation of the changes of cellulases, microorganism. substrate and their mutual functions, the mechanisms of the stimulatory effect of rhamnolipid on rice straw hydrolysis were investigated. The study found that the addition of rhannnolipid increases the activity of p-glucosidase but stabilizes Cel7A activity. The observed results might be the main mechanisms triggering the stimulatory effect of adding biosurfactants on rice straw hydrolysis. Meanwhile, zeta potential of the substrate increased, which could make the resistance of the cell attached to the substrate weaker. This in turn could facilitate easy adhesion and better retention of the microbial cell in the media. Moreover, we discovered that lignin content played an important role in the stimulatory effect of adding rhamnolipid. The adsorption of rhamnolipid biosurfactant prevented unproductive binding of enzymes to lignin. This could be another important mechanism responsible for the stimulatory effects of adding rhannnolipid on rice straw hydrolysis. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved