Described is a process for preparing phenylacetic acid using phenylalanine as a starting material by means of first culturing one or more organisms from the genus Pseudomonas or from the genus Comamanas or mutants thereof; then intimately contacting the organism culture with racemic phenylalanine or L-phenylalanine or a mixture thereof in the presence of a gaseous oxygen-containing composition such as air and in aqueous media; and finally recovering phenylacetic acid from the fermentation broth.