Effects of glass flakes on physical and anti-corrosive performance of thick coating based on unsaturated polyester resin was investigated. In this report, physical properties and corrosion resistance were tested at various concentration ratios and particle sizes of glass flakes, comparing with the system unfilled with pigment or filled with talc. Filling glass flakes to the coating system improved impact resistance extremely. Especially, when large particle size glass flakes were filled at high concentration, high impedance of the film was still maintained and no blisters were observed after the period of immersion test under gradient of temperature (high, 98°C-low, 15°C) in 3 wt. per cent NaCl solution. Additionally, silane coupling agent contributed greatly to impermeability of the film filled with glass flakes.