Hazelnuts were lye peeled and the peeling time (2-12 min), temperature (63-97degreesC) and NaOH concentration (40-140 g NaOH kg(-1) peeling solution) effects on peeling and quality were investigated. Increases in both temperature and concentration of lye solution led to a decrease in peeling time. Moisture content of samples were changed significantly (P<0.05) after the peeling process due to absorption of water. Peeling affected oil and fatty acid contents, peroxide number and colour of the hazelnuts when compared to the untreated samples. By considering the change in quality parameters, the peeling process was optimized using response surface methodology. In optimization studies, the amount of residual NaOH and penetration depth in hazelnuts were also considered. Time was found to be the most significant factor affecting responses. A suitable lye peeling condition was determined as 58.5 g NaOH kg(-1) peeling solution, 94.9degreesC and 2.9 min peeling time. This combination resulted in peeling >98%, 0.45 mm penetration depth, 7.1 g titratable NaOH kg(-1) and a Hunter-L value of 52.93. The quality parameters of peeled hazelnuts at this given combination, such as protein, oil, free fatty acid, ash contents, peroxide number and L values showed no significant change if compared with untreated control samples.