In order to improve theoretical prediction of propeller induced pressure fluctuations, it is indispensable to investigate the behaviour of unsteady cavity on the propeller blades, since the pressure fluctuations are roughly in proportion to the second time derivative of the cavity volume. To this end, several methods of measuring cavity shape have been proposed such as using stereo photography, pin gauge and laser beam scattering. This paper describes a highly advanced method of measuring the three-dimensional cavity shape using a laser beam coupled with a CCD (Charge Coupled Device) camera and image processor to make measurement faster and more detailed. Model experiments on two propellers-a conventional and a highly skewed propeller-of a training ship SEIUN-MARU have endorsed the usefulness of the present measurement technique both in its speed and accuracy. Further, some features of cavity behaviour of highly skewed propellers have been found in terms of cavity thickness distribution and its variation over the blades and the blade angle positions.