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 ($11.48;{mu}g$/mL) showed more excellent free radical (1,1-diphenyl-2-picrylhydrazyl radical, DPPH) scavenging activity (FSC50) than those of leaf and stem extracts ($17.45;{mu}g$/mL). Reactive oxygen species (ROS) scavenging activity (OSC50) of Cosmos bipinnatus extracts on ROS generated in $Fe^{3+}$-EDTA/H2O2 system were investigated using the luminol-dependent chemiluminescence assay. The ethyl acetate fraction of Cosmos bipinnatus flower extract ($0.56;{mu}g$/mL) showed 3 times more excellent ROS scavenging activity than L-ascorbic acid ($1.50;{mu}g$/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 ($10sim50;{mu}g$/mL). The inhibitory effect of ethyl acetate fraction of Cosmos bipinnatus flower extract ($62.75;{mu}g$/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 ($226.88;{mu}g$/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.