It has been reported in the literature that the settlement of pile foundations in sand under sustained service loads is time dependent. As this phenomenon is not well understood, an experimental study is conducted to investigate the mechanism of pile creep in sand. In the first part of the study involving centrifuge modelling of piles, the test results show that the pile settlement increases with the logarithm of time and the rate of settlement increase is dependent upon the magnitude of applied load and sand density. The changes in the soil and pile stresses observed from instruments installed in the soil and along the pile shaft reveal that under sustained loads, stress relaxation takes place at and around the pile tip area with consequent stress transfer to the shaft. Associated ground surface settlement shows that creep is related to volumetric compression rather than dilation of sand. The centrifuge test findings are then related to the creep behaviour of sand subjected to one-dimensional compression. Examination of sand particles before and after sustained compression loads reveals that sand grains have been broken with their angular protrusions gradually ground off with time. The phenomena of sand particle breakage and stress relaxation around the pile tip provide evidence for the hypothesis that the observed creep is due to the progressive breakdown of sand particules. Key words: centrifuge models, creep, mechanism, one-dimensional compression, pile, sand.