This paper presents an experimental program to investigate the amplitude of the effect of pile compressibility on the reduction of frictional capacity between downward- and uplift- loading of a single bored pile in sand. For this task, model pipe piles made of three different materials were used in gravity field and in centrifuge apparatus. The amplitude of the reduction was evaluated according to the compressibility parameter η defined by De Nicola and Randolph. The ratio of uplift friction resistance to downward friction resistance reached an asymptotic value as η increases. The experimental curve of the reduction of frictional capacity and η has been found to be different from the analytical one.