A guided-wave acoustic-optic Bragg cell has been fabricated for the first time, to our knowledge, on lithium tantalate. The waveguide is fabricated by dilute melt proton-exchange, and without electrical tuning a maximum diffraction efficiency of 22% has been demonstrated. In addition, the thermo-optic behaviour of the lithium tantalate waveguide has been shown to be similar to that previously demonstrated on titaniumindiffused and proton-exchange lithium niobate waveguides