The objective of this study was to develop a polymer mortar protection block with high strength and durability using unsaturated polyester resin to complement defects of conventional cement mortar protection block. Physical and mechanical properties of the polymer mortar protection block were also investigated. Low absorptivity, high impact strength, and great bending strength of the polymer mortar protection block was compared with those of the conventional cement protection block. In conclusion, the polymer mortar protection block is excellent and useful as industrial products for erosion control works.