A bacterium growing on formaldehyde as a sole carbon source was isolated by the dilution method from an enrichment culture containing formaldehyde. The isolated strain, YK-32, was identified as Pseudomonas sp. by morphological, biochemical, and genetic analyses. Pseudomonas sp. YK-32 completely degraded 0.05% formaldehyde within 24 hrs. The isolated strain had a high level of formaldehyde dehydrogenase activity, which is thought to be one of the important factors for formaldehyde degradation, when cells were cultivated in the presence of formaldehyde.