In order to investigate antimicrobial substances from natural spices, the effects of garlic juice and ginger juice on the growth of microorganisms were investigated. It was showned that garlic juice inhibited the growth of bacteria, yeasts and fungi but ginger juice did not inhibit the growth of bacteria and yeasts. As result of concentration effect of garlic juice on the growth of microorganisms, the higher concentration of garlic juice was employed, the more growth inhibition was obtained. Comparing the specific growth rate at various concentration of garlic juice, the inhibition effect on yeast appeared much higher than that on bacteria.