The steady state creep of Pb-65Sn-1Zn and Pb-65.5Sn-3.4Zn ternary alloys was investigated in the temperature range from 353 to 413 K under different constant stresses. The results of creep characteristics show two deformation regions (below and above 383 K). The strain rate sensitivity parameter (m) has been found to increase by increasing the working temperature up to about 0.53 and 0.64 for the first and second alloys, respectively. The activation energies of steady state creep of the first and second alloys have been found to be 41-59.7 and 40-58 kJ mol(-1), respectively, characterising grain boundary diffusion. Metallographic observations and X-ray analysis have been confirmed that grain boundary sliding (GBS) accommodated by dislocation motion is the important mode of deformation. It was also established that Pb-Sn-Zn ternary alloys show superior superplastic behaviour compared with Pb-Sn binary alloys as a result of its lower melting temperature (T-m), finer grain size, and the multiplicity of types of interphase boundaries. (C) 2002 Elsevier Science B.V. All rights reserved.