The styrene-degrading bacterium Pseudomonas sp. SR-5 exhibited a high styrene removability in a biofilter. However, the styrene removal efficiency (RE) of SR-5 decreased with time. We carried out styrene gas removal in a biofilter inoculated with mixed cultures of SR-5 and other microorganisms to determine the possibility of obtaining an enhanced RE for a long period. The following three inocula were carried out: (i) styrene-degrading bacteria, strains 1 and 3, (ii) a benzoic acid-degrading bacterium Raoultella sp. A, and (iii) wastewater from a chemical company dealing with styrene. These biofilters with mixed SR-5 showed an enhanced RE compared with those with a single culture of SR-5. The complete styrene elimination capacities for ensuring 100% styrene removal in those mixed cultures were 151, 108 and 124 g/m(3)/h, compared with a single culture of SR-5.