The removal efficiencies of organic substrates, nitrogen and phosphorus in the anaerobic-aerobic biological phosphorus removal process were investigated by addition of acetic acid, propionic acid and butyric acid which are normal volatile fatty acids contained in anaerobic digester supernatants. Substrate utilization coefficients for the phosphorus release and uptake were also estimated. The effect of a VFA, which showed higher phosphorus removal efficiency than the other VFAs did, was also studied in an anaerobic-aerobic-anoxic biological nutrient removal process. For the anaerobic-aerobic process added by VFA, the phosphorus removal efficiencies were up to about 68%, 55% and 61% for the reactors of acetic acid, propionic acid and butyric acid added, respectively, which indicates the efficiencies were increased by about 8-21%, comparing to that of 47% for the reactor with no VFA added. There were no significant difference in removal efficiencies for organic substrate and NH_3-N without regard to addition of VFA. However, the removal efficiency of total nitrogen was increased in the case of VFA added, since NH_3-N was less produced. For the anaerobic-aerobic-anoxic process added VFA, the removal efficiencies for NH_3-N and PO_4^3--P were increased by 5% and 13%, respectively, comparing with them in the reactors not added VFA.