Rosmarinicacidmethylester (Ov-8) was isolated form Origanumvulgare. The antioxidant activities of Ov-8 were evaluated by measuring radical-scavenging activities, reducing power, and inhibition of lipid peroxidation, using liposomes and mice tissue. The percentage inhibition, by Ov-8, of the activities of reactive oxygen species (ROSs) in H2O2-treated BNLCL2 cells was about 116.0–82.3% of that in H2O2-treated cells. The ability of Ov-8 to reduce tyrosinase, DOPA oxidase and melanin contents in B16 cells exceeded those of arbutin and l-ascorbic acid. Ov-8 reduced the expressions of the melanocortin-1 receptor (MC1R), microphthalmia-associated transcription factor (MITF), tyrosinase, tyrosinase-related proteins-2 (TRP-2) and TRP-1 in B16 cells. Applying Ov-8-gel to mice increased L∗ and reduced the erythema (E∗) and melanin (M∗) indices in relation to those of the base-gel and untreated groups. These results suggest that Ov-8 exhibits antioxidant and depigmentation activities that may be useful in food additives and in the control of skin pigmentation.