Biologically active carbon (BAC) system was set up in a water plant of South China during January to December 2007, to study the invertebrate community characteristics of BAC filter. Thirty-seven invertebrate species were found, of which 28 belonging to rotifers.Filter operation could lead to an output of invertebrates in high abundances with the filtrate, and the maximum density could reach 5608 individuals/m3. Average abundances in the effluent water increased in 27-33 folds in comparison to the influent water during the sampling period. Invertebrate community succession had the following trend: filter-feeding animals →small benthic invertebrates →large benthic and resistant invertebrates. Abundances of large-sized invertebrates (copepod adult and oligochaete) at bigger-media column were significantly higher than that at small-media column. The results implied the abundant species diversity of invertebrate in BAC filter. The relationship between invertebrate and biofilm still remain to be studied in detail.