Lanthanum tungstates are promising proton conductor materials with applications in several areas, including electrolytes for solid oxide fuel cells and hydrogen gas separation membranes. Here, we report the preparation and optimisation of dense La5.5WO11.25 tapes obtained by the combination of tape casting and reaction sintering. Homogeneous concentrated mixed suspensions of La2O3 and WO3 were prepared in ethanol. All involved parameters, such as zeta potential and particle size of the initial powders, binder/plasticizer content and sintering conditions have been optimised. Sintered tapes were studied by Rietveld analysis of high-resolution laboratory X-ray powder diffraction, scanning electron microscopy and impedance spectroscopy. This study demonstrates that tape casting and reaction sintering is a suitable technique to prepare thin films of lanthanum tungstates in a single step that show good electrical properties.