By growing the population over the world and the industrialization of countries, the energy demand has been increased. At the same time, shortage and depletion of oil resources, has increased attentions towards bioethanol production as a clean and renewable energy resources. Lignocellulosic materials are one of the renewable and low costresources which are abundantly available. In this study, after a physical treatment (chopping) on pine and elm woods, an alkaline pretreatment was performed with 8% (w/v) NaOH at three different temperatures (0, 25, and 80 °C) for 2 h to improve the yields of enzymatic hydrolysis and ethanol production processes. Alkaline pretreatment by increasing accessible surface area for hydrolytic enzymes and decreasing the cellulose crystallinity and degree of acetylation of hemicelluloses, and also delignification, can modify the structure of lignocellulosic materials. To study the effect of the pretreatment, enzymatic hydrolysis was conducted on the untreated and pretreated woods at 45 °C for 72 h with 30 FPU cellulase and 60 IU ?-glucosidase per grams of substrates. Furthermore, simultaneous saccharification and fermentation (SSF) for production of ethanol was done at 36 °C for 72 h using 15 FPU and 30 IU per grams of substrates. The structural properties of the materials were followed by SEM images and FTIR analysis. The results showed decreasing structural uniformity and crystallinity. For both kinds of wood, maximum increase in water adsorption capacity was observed for the pretreated samples at 0 °C. On the other hand, alkaline pretreatment had a significantlyimproved the buffering capacity of the woods. Furthermore, enzyme deactivation that occurred as a result of ineffective adsorption of enzymes on ligninwas investigated by adsorption-desorption analysis. However, no logical relation obtained between adsorbed and desorbed enzymes and enzymatic hydrolysis results. In order to decrease the ineffective adsorption of enzyme on lignin, a non-ionic surfactant, Tween-20, was added to the mixture of enzymes and substrates. Results of hydrolysis showed that the maximum yield for pine and elm woods pretreated at 0°C improved to 18.7 and 71.5%, respectively. Addition of tween-20 increased the maximum enzymatic hydrolysis yields of pretreated pine and elm to 19.6 and 80.1%, respectively. Yield of ethanol production in SSF step for untreated elm wood was 8.4%, while it was increased to 45.8% after pretreatment at 0°C. For the same pretreatment on pine wood, the yield was increased from 8 to 16.4%. Using tween-20 increased ethanol production yield of pine and elm woods to 23.9 and 57.3%, respectively. In the presence of tween-20,maximum amount of enzyme adsorption was 49.6 mg per gram of pine wood while the maximum amount of desorption was 44.1%. Key Words Alkali pretreatment, Elm wood, enzymatic adsorption, enzymatic desorption, ethanol,hemicellulose,lignin,Pine wood.