This paper presented an experimental study on piezoelectric impedance based prestress force monitoring for prestressed concrete (PSC) beam. The low cost piezoceramic (PZT) patch was attached at the beam firstly and different levels of prestress force were applied to the tendons. The electro-mechanical impedance (EMI) spectra of surface bonded PZT patch were then collected using an impedance analyzer by sweeping the frequency. The statistical index RMSD is then adopted to quantify the variation of EMI spectra due to the variation of prestress force. The relationship between the prestress force and the RMSD index is established. The results show that the EMI technique is a practical and reliable nondestructive test method for prestress force monitoring.