The present paper investigated phosphorus forms in the extracellular polymeric substances (EPS) using 31P-NMR spectroscopy,and analyzed the influential parameters for this method.The results showed that in the three investigated EPS samples five P forms were identified,including orthophosphate,orthophosphate monoesters,DNA,pyrophosphate and polyphosphate.And in the EPS extracted from A/A/O sludge and A/A/O-MBR sludge polyphosphate was the main phosphorus form.This indicated that P is contained in the EPS not only owing to the adsorption of orthophosphate,but also because EPS acting like the bacteria cells contributes to enhanced biological phosphorus removal. Furthermore the transformation of P forms in the EPS during the EPS extraction was found but limited within 1 h.It was found that with the NaOH solution added the polyphosphate in the EPS would partly convert to pyrophosphate but not go further to orthophosphate,while with pure water added P forms in the EPS were very stable.This means that after neutralization,the transformation of phosphorus forms could be avoided.Since the measurement of 31P-NMR spectroscopy was very sensitive to pH,which could affect the chemical shift of the peaks and cause peaks overlapping,the pH of EPS sample must be raised to 13.0 before the measurement.