The leaves of Sasa quelpaertensis Nakai were extracted with 80% ethanol and further partitioned with n-hexane, chloroform, ethyl acetate, n-butanol, and aqueous fractions to evaluate the biological activity through assessment via various in vitro assays, including total phenol content; 1,1-diphenyl-1-picrylhydrazyl (DPPH) and 2,2-azino-bis-(3-ethylbenzothiazothiazoline-6-sulfornic acid (ABTS) radical scavenging; reducing power; α-glucosidase and tyrosinase inhibitory; and alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) activity assays. The highest activity was found in the ethyl acetate fraction for all assays and showed stronger DPPH radical scavenging, reducing power, and tyrosinase inhibitory activity than the positive controls (butylated hydroxytoluene, α-tocopherol, and arbutin, respectively). When compared to the ethyl acetate fraction, the n-butanol fraction had lower rates, but it still demonstrated relatively high activity. The activity of the n-hexane fraction was high for DPPH and ABTS radical scavenging activity and contained significant amounts of phenol content, whereas the chloroform fraction possessed the highest reducing power, tyrosinase inhibitory, and ADH and ALDH activity, despite having the lowest phenol content when compared to the other fractions. These findings clearly indicate that S. quelpaertensis Nakai leaves can be a good natural source of antioxidants and tyrosinase inhibitors, as well as ADH and ALDH activity inducers, suggesting that may have potential for treating various diseases and improving human health.