Cytotoxicities of four urushiols, congeners isolated from the sap of Korean lacquer tree (Rhus vernicifera Stokes), to 29 human cancer cell lines originated from 9 organs were evaluated. Their values of 50% growth inhibition were below $4{mu}g/ml$, and showed cell line specific cytotoxicity. The present results is the first report on the cytotoxicity of urushiols suggesting that they would have an anticancer activity to human cancer cells.