Growing concerns regarding depletion of oil resources, environmental impacts, fluctuations in petroleum products market, and increasing demand for energy have promoted extensive research in renewable and clean alternative fuels. Production of ethanol from lignocelluloses, i.e., sustainable inexpensive resources, is a promising solution to such problems. However, lignocelluloses have recalcitrant nature and need a pretreatment process for the improvement of their bioconversions. In this study, a wide range of leading pretreatments were carried out to effectively produce a concentrated fermentable sugar solution. Poplar as a hardwood, pine as a softwood, and rice straw as an agricultural residue were subjected to autohydrolysis, sulfuric acid, phosphoric acid, hot and cold sodium hydroxide and sodium carbonate pretreatment. The most influencing properties of the lignocelluloses, including crystallinity, porosity, water swelling capacity, and buffering capacity, were measured for both untreated and treated substrates to investigate fundamental changes in the structure by the pretreatments. Enzymatic hydrolysis using commercial cellulases was conducted at 45°C for 72 h. The results showed that the highest glucose yield for poplar and pine woods were 84.0 and 94.2%, respectively, both obtained after phosphoric acid pretreatment, where it was 94.5% for rice straw obtained after cold sodium hydroxide pretreatment. The experiment also demonstrated that the highest initial hydrolysis rate of 17 g/l.h. was obtained after phosphoric acid pretreatment. Ethanol production yield by simultaneous saccharification and fermentation (SSF) was increased by 304 and 274% for poplar and pine, respectively, obtained after phosphoric acid pretreatment, where it was increased by 75% after hot sodium hydroxide pretreatment. The changes of crystallinity indices based on FTIR and XRD analysis did not fully agree with each other. Phosphoric acid pretreatment resulted in the greatest reduction in the crystallinity index. Nevertheless, according to FTIR analysis, this parameter was at the minimum when cold sodium hydroxide was used for the pretreatment of poplar and rice straw and phosphoric acid for the pretreatment of pine. Sodium carbonate succeeded to dramatically improve porosity and raised specific surface area to 130.9 and 160.3 m 2 /g in poplar and rice straw samples, while phosphoric acid lowered it to 51.2 and 43.9 m 2 /g, respectively. Water retention value reached its maximum and minimum values by applying phosphoric acid and sulfuric acid pretreatment, respectively. All pretreatments, particularly the alkaline types, were able to considerably increase resistance against pH reduction. Crystallinity index, based on XRD, strongly depended on the amount of amorphous cellulose. Moreover, similarity between rise and fall of water swelling capacity and crystallinity index was observed. Initial hydrolysis rate was significantly affected by water retention value and crystallinity in poplar and pine woods. Keywords : Crystallinity, Enzymatic hydrolysis, Ethanol, Lignocellulose, Pretreatment