Abstract In order to obtain a better understanding of the underwater explosion phenomena related to emulsion explosives, optical measurements using the water tank technique and cylinder expansion test were carried out. Streak photographs were taken using an image converter camera with a usual shadow graph system. Four kinds of emulsion explosives differing in aluminium contents were used in the experiments. These emulsion explosives were placed into copper and PMMA pipes. From the results obtained with the water tank technique, it is recognized that the maximum velocity of underwater shock wave in the case of a copper pipe is about 10% faster than that in the case of a PMMA pipe. From the cylinder expansion test, it is found that the degree of radial displacement of a copper case (Uexp) increases with increased aluminium content and that in the range of more than 10 wt.%, Uexp decreases with increased aluminium content.