Hazelnut shells are lignocellulosic by-products of hazelnut processing. As the shells are rich in cellulose and hemicellulose, they have high potential as a raw material for production of food enzymes, biofuel, and various chemicals (acetic acid, furfural and lignin degradation products) after bioprocessing. The objective of this study was to determine the effect of alkali pretreatment and enzymatic hydrolysis on production of fermentable sugars from hazelnut shells. The hazelnut shells were pretreated with sodium hydroxide (NaOH) at concentrations of 3-7 % (w/v) for 30-90 min at 121 C-A degrees. Pretreatments were evaluated measuring delignification, solid recovery and production of reducing sugars after enzymatic hydrolysis of the pretreated biomass. Up to 20 % lignin removal was achieved and the highest reducing sugar yield of 318.3 mg/g pretreated biomass (or 91.7 % enzyme conversion efficiency) was obtained from biomass pretreated with 3 % NaOH at a solid to liquid ratio of 1:20 for 60 min. The response surface model predicted the optimal reducing sugar production (357.2 mg/g pretreated biomass) under 3 % NaOH, 1:13 of solid to liquid ratio and 63 min of pretreatment period at 121 degrees C. Overall, the results of this study show a promise for hazelnut shells to be used in production of value-added products.