This study was carried out in order to estimate the residual amount of mercury in soy-bean sprouts in each steps of cooking. Samples were taken at markets and also cultured at home without applying the mercury containing pesticides as control. Mercury was determined by dithizone method. It was disclosed that soy-bean sprouts purchased at markets contained $1.32{pm}0.274ppm$, 13 times as high as the maximal allowable concentration of mercury in food recommeded by Ministry of Health and Social Affairs. Mercury contents, however, dropped off steadily by steps of cooking: rinsed with distilled water and boiled in distilled water showing concentrations of $0.11{pm}0.025ppm$ in boiled sprouts and $0.03{pm}0.022ppm$ in sprout-soup. These values were not statistically different from those in control samples, and not exceeded the maximal allowabled levels of mercury in food. It can be concluded that the use of mercury containing pesticides in the cultivation of soy-bean sprouts is not so serious problem as it has been suspected in respect of food contamination, but careful attention must be paid to indiscriminate use of mercury containing pesticides as they may contaminate air, water and soil and secondarily bring harm to human health through food chains.