In the course of screening for the antimicrobial compounds contained in edible materials, we isolated falcarindiol from celeriac ( Apium graveolens L. var. rapaceum (Mill.) DC). The structure of falcarindiol was identified by EI-MS and NMR spectral data (1-D (¹H- and ¹³C-NMR) and 2-D (¹H-¹H COSY, HMQC and HMBC). To our knowledge, this is the first report on the presence of falcarindiol in celeriac. Two microbial organisms ( Bacillus megaterium and Microbacterium foliorum ) were isolated and identified as food contaminants, and the antimicrobial activities of falcarindiol against these organisms were tested. Falcarindiol showed more potent antimicrobial activity than sorbic acid which is used as a food additive.