An optical bistable device based on Eaman-Nath acoustooptic diffraction is reported. Intensity curves of diffracted light from a Raman-Nath acoustooptic modulator are recorded. The bistability of the first-order diffracted light intensity as a function of the input intensity is presented. Three modes of operation are possible for this acoustooptic bistable device. As a potential application, the acoustooptical bistable device can be used as a multi-channel switch.