In order to investigate biological properties of the dominant strain from the biological activated carbon (BAC) filter column, a novel, dominant iron-and-manganese removal strain, FM-2, was screened from BAC mature biological membrane. By phylogenetic analysis based on 16S rDNA sequence comparison, FM-2 was identified to be Citrobacter freundii. The experimental results indicated that Citrobacter sp. FM-2 could remove 83.6% Fe (II) and 64.9% Mn (II) after four days. Inoculum greatly influenced the iron-manganese removal performances. The appropriate inoculum concentration was 5%. The initial concentrations of Fe (II) and Mn (II) had little negative influence on its removal performance. When Fe (II) and Mn (II) concentrations were 32.9~85.7 and 25.7~46.7 mg/L, respectively, the removal of Fe (II) and Mn (II) followed the first-order dynamical model with the velocity constants of 0.8528~0.9937/d and 0.3001~0.3179/d, respectively.