In this work, the stem bark powder of Hesperethusa crenulata or Thanaka was extracted with organic solvents and water, and investigated the biological activities including antioxidant, anti-tyrosinase, UV screening, antibacterial and anti-inflammatory. Safety of the extracts and original powder were also done by cytotoxic and genotoxic assay. The hexane, dichloromethane, ethyl acetate, methanol, 85% (v/v) ethanol and water extracts of the bark showed some variation between them in terms of their potency of those biological activities. All six solvent extracts and the original crude bark powder showed non-genotoxicity in the assay carried out here. Nevertheless, the methanol, 85% (v/v) ethanol and water extracts of the bark all exhibited a very low cytotoxicity. Moreover, vanillin and acrylate derivative, were obtained from thanaka stem bark.