Mixed juices with fruit and vegetables have been a trend because of different bioactive compounds and sensorial characteristics. Furthermore, the consumer's healthy concern improved the interest in incorporating ingredients with the allegation of functional properties, such as fructooligosaccharide (FOS), in new products. Pasteurization is a common method applied to juices processing but, due to high temperatures, can reduce the content of bioactive compounds. The study aimed to evaluate the impact of ultrasound application to bioactive compounds and antioxidant capacity on orange and beet mixed juice. Mixed juices were prepared in a 7: 3 (v/m) orange juice and carrot with 3.2% FOS. Pasteurization (90°C/1 min) and ultrasound (40 kHz) at 40°C, 50°C, and 60°C for 5 min were applied and after treatments samples were stored for 25 days at 6°C. High-performance liquid chromatography was used for ascorbic acid quantification. Spectrophotometric methods are used for phenolic compounds and antioxidant capacity with the Folin-Ciocalteu reagent and the DPPH radical test, respectively. ANOVA and regression analysis were conducted using the SAS® online software. Treatments applied did not interfere significantly (p>0.05) in antioxidant capacity, phenolic compounds, and ascorbic acid and present mean equal 39.14%, 145.99 mEq of gallic acid/100 mL, and 6.91 mg of ascorbic acid/ 100mL of juice, respectively. However, storage time significantly reduced the ascorbic acid content. The reduction may occur due to the actions of residual enzymes. Nevertheless, at the end of the storage, orange and beet mixed juice with prebiotic beet treated and non-treated presented 72.56% ascorbic acid retention and was considered rich in this nutrient to meet 15.35% of the daily need of ingestion. Bioactive compounds are attractive compost for health for beneficial activities. Thus, mild temperatures combined with ultrasound could be an alternative in processing mixed juices to preserve bioactive compounds.