The antioxidant activity of mung bean sprouts was studied in this research. Active ingredients in different lengths of mung bean sprouts were extracted with water. Concentrations of the main proteins and polyphenols were determined. Antioxidizing capacities of the extracts were measured in vitro using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging test, ferric reducing antioxidant power method, and chelation abilities of ferrous ion. The safety of the extracts was determined using the red blood cell (RBC) test, chick chorioallantoic membrane (CAM) assay, and human skin patch test. Results show that DPPH radical scavenging rates at different shoot lengths were all greater than 85%, while the total antioxidant capacity of the extracts reached more than 4.0 and the chelation abilities of first-day sprout extract is nearly 80%, indicating that mung bean sprouts have excellent anti-oxygenic property. Results of RBC (hemolysis ratio), CAM (vascular morphological), and human skin patch tests (changed subjects) illustrated extracts of mung bean sprouts are safe and can be used as additives in antiaging cosmetic products.