We assessed the susceptibility of three fumigants on Phthorimaea operculella, which is an important pest of stored potato worldwide. 5 to 6 initial dosage of each fumigants were treated on every growth stages of P. operculella. Methyl bromide showed 100% mortality at CT 33.40mg h/ L on egg, CT 14.41mg h/L on late larvae, CT 31.89mg h/L on pupae and CT 16.01mg h/L on adult, respectively. The LCT50 of methyl bromide was 19.115mg h/L on egg, 3.934mg h/L on late larvae, 13.810mg h/L on pupae and 6.260mg h/L on adult, respectively. In case of phosphine, 98% mortality was achieved at CT 16.77mg h/L on egg, and 100% mortality was achieved at CT 16.58mg h/L on late larvae, CT 18.54mg h/L on pupae and CT 12.28mg h/L on adult, respectively. The LCT50 of phosphine was 1.457mg h/L on egg, 2.236mg h/L on late larvae, 1.282 mg h/L on pupae and 0.253mg h/L on adult, respectively. In case of ethyl formate, 100% mortality was achieved at CT 96.21mg h/L on egg, CT 101.30mg h/L on late larvae, CT 120.66mg h/L on pupae and CT 148.30mg h/L on adult, respectively. The LCT50 of ethyl formate was 23.730mg h/L on egg, 13.706 mg h/L on late larvae, 29.578mg h/L on pupae and 19.235mg h/L on adult, respectively.