The influences of vitamin B₁₂ (VB₁₂), a biocatalyst, on the reductive degradation of 8:2fluorotelomer alcohol (8:2FTOH) in anaerobic activated sludge were investigated. VB₁₂ could change the dynamic characteristic of reductive degradation of 8:2FTOH by anaerobic activated sludge and enhance the final removal rates of 8:2FTOH, but there were the upper and the lower dosage limits for the VB₁₂. The final removal rates of 8:2FTOH in anaerobic activated sludge could not be enhanced while the spiked dosage of VB₁₂ was less than or equal to 1mg/L, but no further improvement was also observed when the VB₁₂ concentration was increased to more than or equal to 5mg/L. The final defluorination rates of 8:2FTOH could be significantly inhenced with spiking all VB₁₂ dosages in the present study. The influences of VB₁₂ dosages on the removal rates and defluorination rates of 8:2FTOH in the anaerobic activated sludge were inconsistent. In addition, when the anaerobic activated sludge was amended with the higher concentrations of VB₁₂, the accumulation of intermediate degradation products (i.e. polyfluorinated compounds) was generally inhibited and the lower total molar recoveries of 8:2FTOH were observed while the molar yields of final degradation products (i.e. perfluorocarboxylates), as well as the mineralization defluorination rates of 8:2FTOH, were enhanced.