The objective of this study was to investigate the effects of the main process parameters on supercritical fluid extraction of walnut (Juglans regia L.) kernel oil. The recovery of walnut kernel oil was performed in a green and high-tech separation process. CO2 and CO2 + ethanol mixtures were used as the supercritical solvent. The extraction was carried out at operating pressures of 30, 40 and 50 MPa, operating temperatures of 313, 323 and 333 K, mean particle sizes of 1.78×10−4, 3.03×10−4, 4.78×10−4, 7.00×10−4 and 9.00×10−4 m, supercritical CO2 (SC CO2) flow rates of 1.67×10−8, 3.33×10−8, 6.67×10−8 and 13.33×10−8 m3/s and entrainer (ethanol) concentrations of 2, 4, 8 and 12 vol-%. Maximum extraction yield and oil solubility in SC CO2 obtained at 50 MPa, 333 K, 9.00×10−4 m, 3.33×10−4 m3/h were 0.65 kg oil/kg of dry sample and 37.16 g oil/kg CO2, respectively. The results obtained in this study showed that the crossover pressure effect of walnut kernel oil was at 30 MPa. At 30 MPa and 313 K, the obtained extraction yields above 4 vol-% ethanol reached the organic solvent extraction yield of 68.5 kg oil/kg dry sample. Extraction time was decreased significantly because of the higher solubility of walnut kernel oil in SC CO2 + ethanol mixtures.