The invention discloses a method for manufacturing an extract of Rhinacanthus nasutus (L.) Kurz in order to obtain the extract of Rhinacanthus nasutus (L.) Kurz with improved contents of active ingredients, wherein the method comprising the steps of: soaking a raw sample of Rhinacanthus nasutus (L.) Kurz with a processing reagent at 22 to 37° C. for 12 to 36 hours; boiling the soaked product at 1 atm, 95 to 105° C. for 15 minutes to 1 hour to obtain the processed sample of Rhinacanthus nasutus (L.) Kurz; extracting the processed sample of Rhinacanthus nasutus (L.) Kurz by 95% ethanol at 50° C.