Carbon foam-a kind of new engineering material as packing material was adopted in three biofilters with different pore dimensions and adapted autotrophic nitrite nitrobacteria to investigate the purification of nitric oxide (NO) in a gas stream. The biofilm was developed on the surface of carbon foams using nitrite as its only nitric source. The moisture in the filter was maintained by ultrasonic aerosol equipment which can minimize the thickness of the liquid film. The liquid phase nitrification test was conducted to determine the variability and the potential of performance among the three carbon foam biofilters. The investigation showed that during the NO2--N inlet concentration of 200 g(.)L(-1.)min(-1) to 800 g(.)L(-1.)min(-1), the 24PPC (pores per centimeter) carbon foam biofilter had the greatest potential, achieving the NO2--N removal efficiency of 94% to 98%. The 8PPC and 18PPC carbon foam biofilters achieved the NO2--N removal efficiency of 15% to 21% and of 30% to 40%, respectively. The potential for this system to remove NO from a gas stream was shown on the basis of a steady removal efficiency of 41% to 50% which was attained for the 24PPC carbon foam biofilter at specified NO inlet concentration of 66.97 mg(.)m(-3) to 267.86 mg(.)m(-3) and an empty-bed residence time of 3.5 min.