In this study, the cellular protective effect, antioxidative property and component analysis of Euphorbia humifusa extracts were investigated. The ethyl acetate fraction ($3.68;{mu}g/mL$) and aglycone fraction ($3.15;{mu}g/mL$) of Euphorbia humifusa extract showed prominent free radical (1,1-diphenyl-2-picrylhydrazyl, DPPH) scavenging activity ($FSC_{50}$). Reactive oxygen species (ROS) scavenging activity ($OSC_{50}$) of Euphorbia humifusa extract on ROS generated in $Fe^{3+}$-EDTA/$H_2O_2$ system was investigated using the luminol-dependent chemiluminescence assay. The ethyl acetate fraction ($0.43;{mu}g/mL$) and aglycone fraction ($0.35;{mu}g/mL$) of extract showed higher ROS scavenging activity than L-ascorbic acid ($1.50;{mu}g/mL$). The cellular protective effects of fractions of Euphorbia humifusa extract on the rose-bengal sensitized photohemolysis of human erythrocytes were investigated. The ethyl acetate fraction and aglycone fraction of extract protected cellular membranes against ROS in a concentration dependent manner ($5{sim}25;{mu}g/mL$), and was more effective than (+)-${alpha}$-tocopherol, lipid peroxidation chain blocker. Aglycone fraction from Euphorbia humifusa extract showed 2 bands in TLC and 2 peaks in HPLC. In HPLC chromatogram of aglycone fraction, peak 1 and peak 2 were identified as quercetin and kaempferol, respectively. And these components are very effective as antioxidant. Thus, these results indicate that fractions of Euphorbia humifusa extracts can function as antioxidant in biological systems, particularly skin exposed to UV radiation by scavenging $^1O_2$ and other ROS, and protect cellular membranes against ROS. Fractions of Euphorbia humifusa extracts can be applicable to new functional cosmetics for antioxidant.