The contents of alkaloids in raw Cho O(Aconiti Ciliare Tuber) and its processed products were determined by high performance liquid chromatography. Processing methods 1 and 2 lowered the contents of alkaloids more than the method 3. Cho O processed with method 1 or 2 showed even lower alkaloid contents than commercially available Processed Aconiti Tuber Powder(PATP). The contents of aconitine and hypaconitine in MeOH extracts of Cho O treated with method 3(10 min irradiation) and mesaconitine of Cho O treated with method 3(5 min) were comparable to those of PATP.