Agroindustral residues represents an alternative source for obtaining fermentable products, such as glucose, with higher energy value. Therefore, in this work the isolation of a microorganism with cellulolytic capacity is carried out. A fermentation test of wheat straw with physical pretreatments (grinding), and the combination of a chemical pretreatment —using a saturated solution of Ca(OH)2— with a physical one, combining three particle sizes for the wheat straw were proposed. The results showed that the combination of particle size (141 µm ~ 250 µm) with the chemical pretreatment had a positive effect on biological consumption-degradation of 79.5% and a biomass/substrate yield of 0.49 g/g was observed. Both particle size and alkaline treatment had no significant effect on the cellulolytic activity of the obtained extract (p > 0.05).