The purpose of this work was ultrasound‐assisted extraction of red quinoa carotenoid, and antioxidant effect of the purified carotenoid on soybean oil stability was compared with that of commercial carotenoid. Red quinoa carotenoid was extracted using 50 ml ethanol as the solvent in an ultrasonic bath at 45 ± 1°C and 20 kHz for 3 min. After the carotenoid purification, its effect on the oxidative stability of soybean oil was compared with that of commercial β‐carotene during 8 days of storage at 60°C. Peroxide value (PV), conjugated diene value (CV), thiobarbituric acid (TBA) value, and color parameters were measured. 100 mg/kg of the commercial and natural carotenoids was the best concentration to decrease the TBA value during the 8 days of storage, compared with the other concentrations (200 and 300 mg/kg). On the last day, the samples containing 100 mg/kg of the commercial and natural carotenoids had the lowest CV, and TBA value, and lowest PV was in samples containing 200 mg/kg. In addition, the lowest PV (7.8 meq/kg) was obtained on the eighth day, owing to the performance of β‐carotene at 200 mg/kg, while the samples free of the carotenoids had the highest PV, CV, and TBA value. The samples containing the commercial antioxidant had higher b* values than those with the natural antioxidant because the commercial β‐carotene was yellower than the natural carotenoid. The samples containing the commercial carotenoid had lower a* values than those containing the natural one. Carotenoid extracted from red quinoa could influence the oxidative stability of soybean oil. Practical applications The oxidation of fats and oils can be inhibited by using natural and synthetic antioxidants. Antioxidants, which are considered food additives, are used in the food industry to extend the shelf‐life and prevent the oxidation and degradation of edible oils. The legally allowed antioxidants to be used in edible oils are carotenoids, ascorbic acid, and tocopherol, which are more accepted by consumers than synthetic ones. Red quinoa is a rich source of carotenoids with high antioxidant activity. In this work, high‐intensity ultrasound was used as a non‐thermal and non‐destructive method to improve the extraction rate and efficiency of carotenoids from red quinoa. This technique can be used extensively in the food industry with high economical efficiency.