Leaky surface acoustic waves (LSAWs) and longitudinal-type LSAWs (LLSAWs) have a number of beneficial characteristics such as a larger electromechanical coupling factor K2 and higher phase velocity than those of Rayleigh-type SAWs. However, LSAWs and LLSAWs have inherent attenuation because they lose energy by continuously radiating bulk waves into the substrate. To solve this problem, the authors previously reported that the attenuation of LSAWs and LLSAWs can be reduced by loading with an aluminum nitride (AlN) thin film with a higher phase velocity than that of the substrate [1,2]. However, K2 is reduced owing to the small piezoelectricity of the AlN thin film. In this study, to obtain a substrate structure with a higher K2, the propagation properties of LSAWs and LLSAWs on a LiTaO3 (LT) thin plate bonded to a quartz substrate were investigated experimentally.