The effect of pH on the minimum inhibitory concentration (MIC) of glycerol monolaurate (monolaurin) against four strains of Listeria monocytogenes at 35°C in tryptic soy broth supplemented with 0.6% yeast extract was investigated. Our results demonstrate that the MIC of monolaurin was lower than MIC values reported for other common food antimicrobials such as potassium sorbate, tertiary butylhydroquinone, propyl paraben, and butylated hydroxyanisole. The MIC of monolaurin was reduced by decreasing the pH value of the medium. A 3-fold MIC reduction occurred when the pH decreased from pH 7.0 (10 μg/ml) to pH 5.0 (3 μg/ml).