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The purpose of this paper is to explore theoretically the band structures for different kinds of point defect in phononic crystal thin plates for square / triangle lattice using the improved plane wave expansion method combining with the supercell technique. The defect is created by several means such as changing the radius, the mass density, the elastic modulus, the geometric shape of one of the cylinders, etc. The phononic crystal thin plate is composed of parallel cylindrical inclusion of Al2O3 embedded periodically in the Epoxy host. The results show that the defect modes existing in the first band gap are strongly dependent on the size and the mass density of the point defect for the two lattices. Elastic modulus point defect could not lead the generation of the defect bands for the square lattice. However, for the triangle lattice, the elastic modulus has some influences on the defect modes. With decreasing of the size of the defect, all defect bands move from the upper edge of the first band gap towards the middle and the edges of the first band gap almost remain unchanged as the defect size varies.