Gallic acid and ellagic acid have been identified in the seed of Cornus officinalis by the use of an ultrahigh performance liquid chromatography (UHPLC) method coupled with a diode array detector (DAD). The water extract of C. officinalis seed contained the highest gallic acid content (3.03 +/- 0.10mg/g seed), which was followed by aqueous methanol extract (2.43 +/- 0.10mg/g seed) and aqueous ethanol extract (1.53 +/- 0.25mg/g seed). But a higher concentration (12.32 +/- 0.45mg/g seed) of ellagic acid was obtained from extraction with aqueous methanol than with aqueous ethanol (11.03 +/- 0.42mg/g seed) and water (7.28 +/- 0.16mg/g seed). After heat treatment and acid hydrolysis, C. officinalis seed had higher concentrations of gallic acid and ellagic acid, contributing to more potent antioxidant activity. The results demonstrated a rich source of gallic acid and ellagic acid in C. officinalis seed, which might provide a novel source of these natural antioxidants.