A passive coaxial pulse shaper has been developed which produces a subnanosecond duration pulse with short rise and decay time from a long pulse with short rise time. The mechanical construction of the pulse shaper is a modified coaxial air line T-section. The pulse shaper has been incorporated in the pulsing circuit of a 3-MV Van de Graaff accelerator. The form of the resulting electron beam pulses was monitored both as the charge collected by a coaxial target and as the Cerenkov light emitted by a quartz plate. In both cases sequential sampling techniques were used. The electron beam pulses were found to have rise and decay tiems of approxiamtely 100 ps and a half-width as short as approximately 200 ps could be obtained. An advantage of this method of producing subnanosecond beam pulses is that it does not interfere with normal nanosecond pulsed operation of the Van de Graaff.