Many studies have shown that bioactive compounds, for example, polyphenols, and so on can play an important role in reducing oxidative stress and protect against various diseases. The sources of these compounds in the human diet include mainly fruit and good quality fruit juices, which may contain polyphenols but also other phytochemicals such as vitamin C. The purpose of the study was to analyze the antioxidant properties of vitamin C-rich juices, which underwent mild processing. The content of total polyphenols (TP, FBBB), total flavonoids (TF), total anthocyanins (TA), and vitamin C as well as the antioxidant capacity (DPPH, ABTS) were evaluated in commercial fruit juices rich in vitamin C (acerola, gojiberry, sea buckthorn, wild rose, cranberry, Japanese quince). Moreover, phenolic acids and selected flavonoids were determined by HPLC methods. Among the examined fruit juices, acerola and wild rose juices contained the highest amounts of vitamin C and total polyphenols, and had the highest antioxidant capacity. Acerola owes its high antioxidant properties mainly to vitamin C, whereas the antioxidant capacity of wild rose is also attributed to its rich content of flavonoids and phenolic acids. Sea buckthorn juice and Japanese quince juice had a lower antioxidant capacity, yet higher than determined for gojiberry and cranberry juices. Total anthocyanins were the highest in cranberry juice. The results showed that the analyzed juices were a valuable source of natural antioxidants. Generally, vitamin C-rich juices are also good source of polyphenols. Vitamin C and polyphenols act synergistically and define the antioxidant properties of juices.