Because of their lightweight, highly crushable and compressible nature, pumiceous sands are problematic from engineering and construction viewpoint. There has been very little information on their liquefaction characteristics and most empirical procedures available in evaluating the liquefaction potential of sands are derived primarily from hard-grained sands. To understand the liquefaction characteristics of pumice sands, several series of monotonic undrained triaxial tests were conducted on commercially-available pumice sands. Results indicated that specimens reconstituted under loose and dense states practically showed similar response, confirming the earlier findings that relative density did not have significant effect on the behaviour of pumice. The stress-strain relations showed a stiffer response at small strain level, followed by development of large strains and greater dilatancy when the phase transformation state (i.e., from contractive to dilative) was reached. Pumice sands have angle of internal friction at failure of about 42-44o, which is much greater than those of natural hard grained sands. Even under large strain level, they did not reach steady state of deformation, possibly due to continuous breakage of particles during shearing, which resulted in more resistant soil structure that did not allow deformation at constant shear stress to occur.