Fourteen strains capable of growing on phthalic acid, iso- and/or tere- phtalic acids as a sole carbon source respectively, were isolated from soil with enrichment culture method. Strain No. 3-31 with an ability to grow on phthalic acid abundantly was selected for further experiments. Ammonium nitrate and ferrous sulfate enhanced the production of cells with high phthalic acid oxidizing activity. Enzymes to metabolise phthalic acid in this strain was inducible. It was required to add 0.05 % phthalic acid before harvest to obtain the large amount of cells with high activity to oxidize phthalic acid. Since cells grown on phthalic acid could not oxidize protocatechuic acid, a new pathway to metabolise phthalic acid was estimated.