In this study, the antioxidative effect, cellular protective effect and inhibitory effect on tyrosinase of Cosmos bipinnatus extracts were investigated. The ethyl acetate fraction of Cosmos bipinnatus flower extract (11.48 μg/mL) showed more excellent free radical (1,1-diphenyl-2-picrylhydrazyl radical, DPPH) scavenging activity (FSC50) than those of leaf and stem extracts (17.45 μg/mL). Reactive oxygen species (ROS) scavenging activity (OSC50) of Cosmos bipinnatus extracts on ROS generated in Fe3+-EDTA/H2O2 system were investigated using the luminol-dependent chemiluminescence assay. The ethyl acetate fraction of Cosmos bipinnatus flower extract (0.56 μg/mL) showed 3 times more excellent ROS scavenging activity than L-ascorbic acid (1.50 μg/mL). The protective effects of the ethyl acetate fractions of extracts from different parts of Cosmos bipinnatus on the rose-bengal sensitized photohemolysis of human erythrocytes were investigated. The ethyl acetate fractions of leaf and stem extract and flower extracts suppressed photohemolysis in a concentration dependent manner (10~50 μg/mL). The inhibitory effect of ethyl acetate fraction of Cosmos bipinnatus flower extract (62.75 μg/mL) on tyrosinase was investigated to assess the whitening efficacy. The ethyl acetate fraction of Cosmos bipinnatus flower extract showed 3.5 times higher tyrosinase inhibitory effect than arbutin (226.88 μg/mL) known as an effective whitening agent. These results indicate that fractions of Cosmos bipinnatus extracts can function as antioxidants in biological systems, particularly skin exposed to UV radiation by scavenging 1O2 and other ROS, and protect cellular membranes against ROS. Fractions of Cosmos bipinnatus extracts can be applicable to new functional cosmetics for antioxidant and whitening.