Combination pretreatment of rice straw using microwave and alkali and its enzymic hydrolysis were investigated and compared with the alkali-alone pretreated process. First, the effect of microwave power and pretreatment time on the weight loss and composition of rice straw was examined. The results show that higher microwave power with shorter pretreatment time and the lower microwave power with longer pretreatment time had almost the same effect on the weight loss and composition at the same energy consumption. The comparison was then made between the effect of the microwave/alkali pretreatment and the alkali-alone one on the weight loss and composition of rice straw. The rice straw had a weight loss of 44.6% and composition cellulose 69.2%, lignin 4.9% and hemicellulose 10.2% after 30-min microwave/alkali pretreatment at 700 W while it only had a weight loss of 41.5% and composition cellulose 65.4%, lignin 6.0% and hemicellulose 14.3% after 70-min alkali-alone pretreatment. It may be that microwave/alkali pretreatment could remove more lignin and hemicellulose from rice straw with shorter pretreatment time compared with the alkali-alone one. Finally, the enzymic hydrolysis of pretreated rice straw (substrate concentration 50 g l(-1), enzyme loading 20 mg g(-1) substrate) was also investigated and the results indicate that rice straw pretreated by microwave/alkali had a higher hydrolysis rate and glucose content in the hydrolysate in comparison with the one by alkali alone. (c) 2005 Elsevier Ltd. All rights reserved.