The objective of this study was to study and compare the effect of particle size on the modified supercritical carbon dioxide and soxhlet extraction in terms of oil yield and antioxidant activity. The mean particle sizes of 300, 355, 425, and 500 µm for modified supercritical carbon dioxide extraction, the temperatures of 40 and 70 °C, pressure of 10 and 30 MPa, flow rate of CO2 3 mL/min, and rate of co-solvent 5% were used in this study. Meanwhile, for soxhlet extraction, the extraction time was 6 hr with ethanol, hexane, and water as the solvent. DPPH method was used to analyze the antioxidant activity of the extract. The results showed that 425 µm gave the highest yield extract on the modified supercritical carbon dioxide extraction (15.53%), soxhlet extraction (36.28%), antioxidant activities for modified supercritical carbon dioxide (93.43%), and soxhlet extraction (62.21%). Single sphere model has successfully fitted the experimental data of modified supercritical carbon dioxide with error below 5% with the highest diffusivity coefficient was 6.794E-12 m2/s at operating conditions was 10 MPa, 40 °C and particle size 425 µm. Practical applications: Peanut skin as waste of peanut industries has many bioactive compounds and high antioxidant activities. Therefore, supercritical carbon dioxide extraction as a green technologhy carry out the extract from peanut skin. Addition of ethanol as modifier is needed to enhance the polarity of supercritical carbon dioxide to extract polar compounds inside of peanut skin. To begin with, the extract of peanut skin using modified supercritical carbon extraction is compared with soxhlet extraction as conventional extraction. Although soxhlet extraction obtained high yield extract, modified supercrirical carbon dioxide gave higher antioxidant activities. The antioxidant activity of modified supercritical carbon dioxide extraction was more than 90%. Furthermore, effect of particle size in the extraction processes was determined to obtain high extract yield and antioxidant activity. the result shows that 425 µm gave the maximum yield extract and antioxidant activity on the modified supercritical carbon dioxide and soxhlet extraction.