The effects of pre-drying on the quality of frying oil and potato slices were investigated. Potato slices were air-dried at 60 degrees C for 15, 30, 45, 60, 90, 120 min before frying. The pre-dried potato slices were deep-fried in sunflower oil at 180 degrees C for 5, 10, 13 min and sampled. For the oil sampling, the frying procedure was repeated five times using dried potato slices without oil replenishment. Oil samples were removed at the end of successive frying operations (13 min-1st, 39 min-3rd, 65 min-5th) and analysed. The moisture content, colour and oil intake of the potato slices and the colour, peroxide value, free fatty acid, fatty acid composition and viscosity of the oil samples were evaluated. Pre-drying treatment had a significant effect on the physicochemical properties of potato slices and frying oil. Pre-drying decreased the oil absorption. The oil content for the 5 min frying was found as 4.46% and 2.93%, respectively, for the control and 120 min pre dried samples. Free fatty acid levels and viscosity of the oil decreased depending on the pre-drying time. The highest level of free fatty acid (0.42%) was found at the end of the 5th frying operation in control samples. The viscosity of oil increased during frying. In control samples, the viscosity of oil was found 82.47 and 85.8 Pa s, respectively, at the 1st and 3rd frying operations. Pre-drying did not affect the fatty acid composition of the frying oil when compared with fresh oil.