In this study, we investigated the anti oxidative potential and protective effects of water extract of Leonurus sibiricus L. leaf (LSLW) against ultraviolet B (UVB)-induced oxidative damage in human keratinocytes (HaCaT cells). To evaluate the anti oxidative activity of LSLW, we measured DPPH radical, hydroxyl radical, hydrogen peroxide, superoxide anion scavenging activities, lipid peroxidation inhibition, and reducing power of LSLW. For induction of oxidative stress in HaCaT cells, the cells were irradiated with UVB at 40 mJ/㎠. To investigate the protective effects of LSLW against UVB, we measured cell viability and apoptotic bodies using annexin V staining. LSLW showed anti oxidative activities by scavenging DPPH radical, hydroxyl radical, hydrogen peroxide, superoxide anion and by reducing lipid peroxidation. In addition, LSLW showed high reducing values. The UVB-induced oxidative conditions led to cell apoptosis. However, treatment with LSLW ameliorated oxidative stress conditions, including inhibition of cell death, apoptotic body. Taken together, LSLW exhibited anti oxidative and protective effects against UVB-induced damage in HaCaT cells. Thus, LSLW could be useful for the development of cosmetics for UVB-induced skin aging.