Frying is considered as a usual method of food processing. However, the use of vacuum during this process is one of the new technologies which is done to improve the quality characteristics of the oil and the fried product. The purpose of this study was to investigate the effect of frying and cooling under vacuum and atmospheric pressure on the quality characteristics of chicken nugget and fried oil. For this purpose, six treatments were considered which among them two treatments were fried under atmospheric pressure and temperatures of 170 °C, and then cooled at atmospheric pressure and 10 kPa. The other treatments were fired at temperatures of 115 and 170 °C and pressure of 10 kPa and cooled at 10 kPa and atmospheric pressure. Then, moisture loss, oil absorption, shrinkage, internal and surface porosity, color, textural properties, oxidation and sensorial characteristics of fried nuggets were evaluated. Also, fried oil was assessed in term of acid and peroxide values, malondialdehyde, fatty acid composition, color, viscosity, and polar compounds of oil. The results were statistically analyzed using completely randomized and split-plot design. Frying and cooling under atmospheric pressure and at the temperature of 170 ° C had undesirable effects on the nugget and oil properties. The treatment led to the enhancement of oil absorption, cooking loss, shrinkage, surface porosity, springiness, redness, yellowness and oxidation in nugget and also increased acidity, polar compounds, viscosity, redness, yellowness, oil oxidation, and reduction of unsaturated fatty acids such as oleic, linoleic and linolenic acid in frying oil. On the other hand, when was performed frying at temperature of 115 °C and pressure of 10 kPa and samples cooled at that pressure, the fried nuggets had the least shrinkage, hardness and also the least oxidation, redness, yellowness and the highest lightness. In these conditions, the lowest acid value, viscosity and oxidation were observed in frying oil. Based on the results, it seems that frying at 115 °C under 10 kPa pressure and cooling in the same conditions have the least undesirable effects on the quality of frying oil, and lead to the lowest oxidation progress in the nuggets. Keywords Frying, Chicken nugget, Vacuum and Atmospheric pressure, Frying oil.