Abstract: The Purification experiments of waste gas containing low concentration toluene were made in trickling biofilter with ceramic spheres.The effects of liquid flow rate, gas flow rate, pH of circulation liquid, and toluene concentration in inlet gas on the purification efficiency of trickling biofilter were investigated.The pressure drop of the trickling biofilter was also measured during experiments. Increasing liquid flow rate and gas flow rate resulted in the decrease of purification efficiency of trickling biofilter.The highest purification efficiency of trickling biofilter was found at the circulation liquid pH of 7.The porosity of the packing material at the inlet of gas was higher than that at the outlet of gas in biofilter after continuous operation in 50 days. The decrease in the porosity of packing material caused a great increase in the pressure drop of the biofilter.