To screen for an anti-yeast substance (AYS), many bacteria were isolated from soil and a strain AY2000 was selected. The strain AY2000 was identified as Rahnella aquatilis by morphology, biochemical properties, and 16S r-RNA nucleotide sequence analyses. The strain AY2000 showed anti-yeast activity against Candida albicans and Saccharomyces cerevisiae, whereas R. aquatilis ATCC33071 as a type strain did not show the activity against the yeasts under the same condition. The growth of yeast cell was significantly inhibited by AYS produced by the strain AY2000, as shown by optical density and MTT assay. The minimum inhibitory concentration (MIC) of the AYS against S. cerevisiae and C. albicans at $28^{circ}C;was;20{mu}g/ml;and;60{mu}g/ml$, respectively. The MIC of AYS against hyphae of C. albicans at $37^{circ}C;was;600{mu}g/ml$. Scanning electron microscopic analysis revealed that yeast cells treated with AYS had an irregular form with a wrinkled and rough surface.