A lithium tantalate substrate obtained by working in the state of a substrate a lithium tantalate crystal grown by the Czochralski method is buried in a mixed powder of Al and Al.sub.2O.sub.3, followed by heat treatment carried out at a temperature kept to from 350 to 600.degree. C., to manufacture a lithium tantalate substrate having volume resistivity which has been controlled within the range of from 10.sup.10 to 10.sup.13 .OMEGA.cm. The substrate obtained has a very low pyroelectricity or no pyroelectricity, and it can be made colored and opaque from a colorless and transparent state and also sufficiently has the properties required as a piezoelectric material.