A novel process was demonstrated for the preparation of an epitaxial Bi0.5Na0.5TiO3 (BNT) single-crystalline film on a SrTiO3 single crystal substrate by simply heating a composite consisting of a BNT powder layer on the substrate. The BNT powder layer was formed on the substrate by spin coating and the composite was heated at 1150°C for several hours in a lidded crucible containing the BNT powder to avoid evaporation of Na and Bi from the composite. This yielded an epitaxial BNT single-crystalline film several micrometers thick. The film had a high degree of orientation with the rocking curve full width at half maximum of 0.064°. The mechanism of film formation was found to be solid-state spreading of BNT powder particles on the substrate, and a dense film was obtained from the porous powder layer.