The aim was to investigate the influence of high‐power ultrasound treatment (HPU) on polyphenolic stability and antioxidant capacity in cloudy apple juice during 7 days of storage at 4°C. HPU (100 W, 30 kHz frequency) was operated at: (i) amplitude 40 versus 80%, (ii) the probe diameter 7 versus 10 mm, and (iii) treatment time of 3, 6, and 9 min. Total phenols (TP), total flavan‐3‐ols (TFL), and in vitro antioxidant capacity (DPPH and FRAP) were determined spectrophotometrically. Findings revealed that HPU significantly decreased TP, TFL, and antioxidant capacity in the samples. However, results indicated that examined sonication parameters, represented as the probe diameter and treatment time, significantly contributed to the stability of TFL. With respect to shelf‐life, the greatest stability of both, polyphenols and antioxidant capacity, was observed in all un‐treated samples, whereas significant lower amounts of TP, TFL, DPPH, and FRAP were found in sonicated samples. Practical applications The global fruit juice market is constantly growing due to the increased consumer preferences toward healthier foods. Consumption of fruit juices, like cloudy apple juice, is a convenient way to get more servings of fruits per day for increased health benefits from dieting. Thermal processing of this juice may negatively influence the nutritive and biological value, so high‐power ultrasound technology (e.g., nonthermal processing), could be useful tool to ensure stability during cold storage. Therefore, enhanced phenolic and antioxidant stability obtained with innovative nonthermal approach is directly related with economic and nutritive cost‐benefits of industrial processing.