Aperiodic arrangement PZT5 fiber/epoxy resin 1-3 piezoelectric composites were fabricated by viscous polymer processing. The impedance spectra were used to discuss the radial and thickness resonance models dependent on the size of 1-3 composites. The aspect ratio t/d is found critical to the resonance parameters. As the aspect ratio t/d reducing, the mechanical quality factor Q(m) would decrease, the frequency constant N-t and the acoustic impedance Z increasing. In general, the composites showed nearly a pure thickness mode with high anisotropy coefficient (k(t)/k(p) similar to 1.38-2.75) and low acoustic impedance (Z similar to 9.5-11.7 Mrayl) superior to those of monophasic PZT5 materials that have potential applications in medical ultrasonic transducers.