Autohydrolysis and dilute-acid hydrolysis were used as pretreatment methods to enhance the enzymatic digestibility of cellulose in two different lignocellulosic substrates, a softwood mixture and an agricultural residue of almond shells. The changes in the chemical composition of the softwood mixture during dilute-acid pretreatment were studied, and the results were grouped by using a severity parameter, KR(OH), which was derived from the kinetics of hemicellulose solubilization. The average degree of polymerization of the cellulose retained in the pretreated substrate, DPv, was investigated and its trend compared with that of almond shells. Cellulose DPv decreased for both the substrates from a value of 700 for the untreated lignocellulosic to around 200, which corresponds to the leveling-off degree of polymerization, as there is no significant variation in DPv when severity increases. Glucose yields after enzymatic saccharification of the pretreated substrates turned out to be higher for almond shells than for the softwood mixture, which had a very low susceptibility to enzymatic hydrolysis throughout the spectrum of experimental conditions investigated. At KR(OH) = 15 000, the glucose yield for the softwood mixture is 44% of the potential fraction present in the pretreated pulp, while for almond shells the maximum yield surpasses 97% for KR(OH) = 3. The different behavior between these lignocellulosic species is not caused by different degrees of cellulose depolymerization nor by the removal of different amounts of carbohydrates during pretreatments in equivalent conditions.