Staghorn sumac (Rhus hirta L) is a native tree in Eastern Canada whose fruit has been used by aboriginal peoples to treat various illnesses, and has recently been found to be a good source of antioxidants. However, the phytochemical composition of R. hirta is not known. In this study, we used Four highly accepted assays and confirmed its FRAP, ORAC, beta-CLAMS and PCL values to be 79.95 mu mol AAE/g DW, 1544 mu mol TE/g DW, RAA 129% and 4513 mu mol TE/g DW, respectively. The antioxidant activities correlated positively to the total polyphenols content, which was higher in the ethanolic extract (81.6 mg GAE/ g DW) compared to the water extract (46.3 mg GAE/g DW), suggesting polyphenols play an important role. Quantitative data from UHPLC and qualitative studies using HPLC-DAD-MS showed that in addition to commonly found phenolic acids, flavonoids and anthocyanins, R. hirta fruit contained a novel group of unique anthocyanins with aglycones (anthocyanidins) at 449, 419 and 433 Da. Further studies on the identification and their health beneficial effects are being conducted.