The content of polyphenols in grapes is high and decreases considerably when they are processed, as their extraction in a juice form. Ultrasound technology (US) has been used as an alternative processing that allows to conserve and preserve the nutritional value of food. The objective of this work was to evaluate the effect of ultrasound on the content polyphenol of grape juice, Isabel cultivar. Juice samples were submitted to different treatments: pasteurization (85 °C/15 minutes), ultrasound (20 kHz, 500 W/15 minutes) and control (no treatment). The determination of total polyphenols in the treated samples was carried out on the day of juice extraction and after 30 days of freezing, and the results expressed in gallic acid equivalent (mg AGE / 100g) (Singleton and Rossi, 1965 adapted). The levels of polyphenols after juice extraction were: 98.40 (pasteurization), 86.59 (US) and 48.04 (control), differing significantly by Tukey's test (p <0.05). However, after 30 days under freezing, the pasteurized juice and the sonicate did not differ (Tukey p> 0.05) in the content of polyphenol, with values above the control sample (65.31, 58.94 and 27.53, respectively). It can be seen that the juice extraction process, without the use of a treatment, presented lower polyphenol contents than that treated by US. The effect of the US can trigger a mechanical stress in the food, stimulated by acoustic cavitation, favoring the rupture of the cell wall and greater dispersion of the substrate matrices, which may have contributed to increase polyphenols in the juice. In addition, the production of free radicals that bind with cell wall compounds, such as polysaccharides or proteins, can increase the levels of phenolic compounds. Therefore, the ultrasound is a viable alternative in the production of juices, cultivar Isabel, without drastically reducing the content of polyphenols.