Onion extracts were tested for effects on the growth and lactic acid production of Lactobacillus bulgaricus in the medium containing mercury. The media containing mercury were added with onion extracts and inoculated with the bacterium and then incubated at $39^{circ}$ for four days. All of the onion extracts examined increased the growth and lactic acid production of the bacterium in the medium containing mercury. At the addition of the edible portion extract of onion to the medium containing 5 ppm, 10 ppm and 20 ppm mercury, the higher the concentration of the onion extract was added, the greater the increasing effect on the growth and lactic acid production. The brown peel extract of onion increased the growth and lactic acid production of the bacterium in the medium containing mercury at all concentrations. The higher the concentration of the extract added, the more effective the increasing effect. The onion solutions of edible portion and brown peel extracted at $90^{circ};to;100^{circ}$ showed more desirable effects than those extracted at the room temperature. Among four kinds of the onion extracts, the brown peel solution extracted at $90^{circ};to;100^{circ}$ was the most effective in increase of the growth and lactic acid production in the medium containing mercury.