ABSTRACT: Garlic oil (GO) and allyl alcohol (AA), both derived from alliin in garlic using different preparation methods, cause potent growth inhibition in yeasts. GO and AA inhibited Candida utilis ATCC42416 in different ways: GO has fungistatic activity while AA has fungicidal activity. GO and AA have almost identical antimicrobial potencies against the indicator yeast, with minimum inhibitory concentrations of about 25 ppm when tested individually. When GO and AA were tested in combination, the antimicrobial efficacy significantly increased. Combinations of AA and GO at 1 and 9 ppm, 2 and 7 ppm, 5 and 5 ppm, and 6 and 3 ppm, respectively, inhibited C. utilis completely. The sum of the fractional inhibitory concentrations (FICs) in the 2-component (GO and AA) combination was as low as 0.37 for C. utilis, indicating strong synergism. The sum of the FICs of diallyl disulfide and diallyl trisulfide in combination with AA was larger than that of the GO–AA combination, suggesting that the synergy was lower.