Porous ceramics of the PZT type have been found to exhibit very high values of piezoelectricgconstant when compared with the conventional PZT. The material also showed no hysteresis effect upon pressure cycling. These features suggested that porous ceramics may be potentially useful for hydrophone applications. Early prototypes of high‐frequency hydrophone designs containing porous PZT elements were found to have a constant free‐field voltage sensitivity (FFVS) up to about 100 kHz. Above this frequency, however, a sharp decrease in the FFVS was observed. Since variations in the hydrophone design did not improve the high‐frequency response of the hydrophones, the loss in FFVS was attributed to the material itself. A theoretical model was developed to analyze this loss phenomenon in porous ceramic hydrophones. The effect of the porosity was found to reduce the frequency constantNRof the piezoelectric ceramic. The frequency dependence of the strain produced in the porous ceramic by a longitudinal wave was further determined. The general feature of the strain‐versus‐frequency calculation agreed very well with the measured FFVS‐versus‐frequency relation. Since the voltage generated is proportional to the strain in the piezoelectric element, this result is used to explain the observed loss in the FFVS of porous ceramic hydrophones. [This work was supported by the ONR Acoustic Transduction Metrology Program.]