Ginseng, referring to the dried roots of Panax ginseng C.A. Meyer, has been known as a famous traditional folkloric medicine in East Asian countries for a long time. In recent years, it has been gaining a worldwide popularity as a dietary herbal supplement. Ginsenosides are bioactive ingredients that are responsible for most pharmacological efficacies of ginseng. Ginsenoside Rg2 (Rg2), one of minor protopanaxatriol (PPT)-type ginsenosides, exists in two epimeric forms, 20(S)-ginsenoside Rg2 [20(S)-Rg2] and 20(R)-ginsenoside Rg2 [20(R)-Rg2]. This work was undertaken to assess and compare their skin anti-photoaging properties. When they were applied to HaCaT keratinocytes prior to the irradiation, 20(S)-Rg2 only could attenuate the UV-B-induced intracellular reactive oxygen species (ROS) elevation, which were detected using three fluorescent ROS dyes, such as 2',7'-dichlorodihydrofluorescein diacetate, dihydroethidium and dihydrorhodamine 123. 20(S)-Rg2 but not 20(R)-Rg2 significantly attenuated the UV-B-induced promatrix metalloproteinase-2 (proMMP-2) gelatinolytic activity and protein levels. Likewise, 20(S)-Rg2 only augmented the UV-B-reduced total glutathione (GSH) and superoxide dismutase (SOD) activity levels in a concentration-dependent manner. Neither of the two Rg2 epimers was cytotoxic to HaCaT keratinocytes, regardless of UV-B irradiation. Taken together, of the two Rg2 epimers, 20(S)-Rg2 only possesses the stereospecific protective properties against the UV-B-induced skin photoaging in HaCaT keratinocytes.