Abstract: Ultrathin LiTaO3 wafer is needed as a sensitive lay for fabricating high performance pyroelectric infrared sensor array. Since the thickness of LiTaO3 wafer was thicker than the required thickness, the LiTaO3 wafer was processed by the novel wafer bonding and mechanical thinning processes, i.e. benzocyclobutene (BCB) bonding, grinding, polishing, heating stripping and BCB etching. The ultrathin single crystal LiTaO3 wafer with dimensions of 10mm10mm25m was prepared with the thinning processes. The pyroelectric coefficient of the thinned LiTaO3 wafer is 1.610-4Cm-2K-1. The measured results of the thinned LiTaO3 wafer show that the thickness uniformity, surface roughness and surface profile accuracy can meet the requirement of the application.