Some quality parameters included, free fatty acids, peroxide value, iodine value, fatty acid composition as well as degree of color darkening were evaluated for mixed vegetable oil during 16 hours at 180 C° of deep-frying process. Both of potato and chicken were used as frying materials for 10 and 15 min., respectively. The results indicated that, there were gradually increase of free fatty acids and decrease of iodine value with the two types of the used foods with increasing of deep frying process time. Peroxide value, recorded initially an increase, then decreased after 14 and 6 hours of frying process of potato and chicken, respectively. During the deep frying process, the total unsaturated fatty acid content of the used oil was decreased while the total saturated fatty acid content was increased. Darkening degree of the used oil color was increased by increasing the use-time of frying process with slightly high of color darkening in case of chicken compared to that of potato frying.