We study the effects of a defect created by metallic coating of the central rod in a square lattice of dielectric rods for TM polarization lights. A calculation using the Plane Wave Expansion Method (PWE) in the supercell model shows that the photonic band structure and field distribution in the defect area varies with changing metallic layer thickness. The optimal energy localization is explored by varying the thickness of the metal layer. Enhancement of the energy confinement is described by the narrower spatial distribution profile of the energy with thicker metal coating. A more quantitative description, given in terms of confinement quality (CQ) defined by the normalized integrated intensity in the central rod, exhibits monotonous increase of CQ with growing metal layer thickness. The highest CQ value achieved is around 80% for a 3 × 3 supercell, which is considerably higher than the 44% optimal value achievable in the same dielectric PC structure with a defective central rod. Further calculation using the Extended Plane Wave Expansion Method for determining the imaginary part of the Bloch wave vector shows increasing with increasing metal coating thickness. The following analysis explains and corroborates the enhanced energy confinement effect.