Simultaneous removal of $NH_3,;H_2S$ and toluene in a contaminated air stream was investigated over 185 days in a biofilter packed with Zeocarbon granule as microbial support. In this study, multi-microorganisms including Nitrosomonas and Nitrobacter for nitrogen removal, Thiobacillus thioparus (ATCC 23645) for $H_2S$ removal, and Pseudomonas aeruginosa (ATCC 15692), Pseudomonas putida (ATCC 17484) and Pseudomonas putida (ATCC 23973) for toluene removal were used simultaneously. The empty bed residence time (EBRT) was 40-120 seconds and the feed (inlet) concentrations of $NH_3,;H_2S$ and toluene were 0.02-0.11, 0.05-0.23 and 0.15-0.21 ppmv, respectively. The observed removal efficiency was 85%-99% for $NH_3$, 100% for $H_2S$, and 20-90% for toluene, respectively. The maximum elimination capacities were 9.3, 20.6 and $17g/m^3/hr;for;NH_3,;H_2S$ and toluene, respectively. The results of kinetic model analysis showed that there were no particular evidences of interactions or inhibitions among the microorganisms, and that the three bio degradation reactions took place independently within a finite area of biofilm developed on the surface of the Zeocarbon carrier.