Adsorption isotherms of raw and roasted (at 100 degreesC, 120 degreesC, 140 degreesC and 160 degreesC) hazelnuts of Tombul variety were determined at 25 degreesC, and over relative humidities ranging from 11 to 90% using the gravimetric static method. Eleven sorption models (GAB, BET, Modified BET, Halsey, Iglesias-Chirife, Oswin, Chung-Pfost, Smith, Kuhn, Harkins-Jura and Caurie) were evaluated by using the linear regression method. GAB (Guggenheim-Anderson-de Beer) model satisfactorily described adsorption characteristics of the samples over the experimental range of study. Monolayer values at 25 degreesC were estimated from the GAB model as 0.0155 kg water/kg dry solid for raw and 0.0100-0.0163 kg water/kg dry solid for roasted hazelnuts. Caurie security moisture content for raw hazelnuts was also determined from Caurie model as 0.048 kg water/kg dry solid.