Boron is known of the powerful pealrite stabilizing elements in cast irons. In this study, to improve the wear resistance of ductile cast iron, a small amount of phosphorus-boron complex additive was added. Five melts having different compositions of phosphorus and boron were tasted into Y-type CO₂mould and inspected thear microstructure, mechanical and thermal properties, respectively. The results obtained from this study are as follows ; 1. Although the wear resistance of ductile cast iron is raised with the addition of B and P, its effect are more remarkable when they areadded simultaneously. For this reason the recommended complex addition amount is in the range of 0.04%B and 0.4%P. 2. Although the hardness of the ductile cast iron is increased with the addition of B and P it`s machinability is improved if additive amount is not over 0.04%B and 0.4%P. 3. The value of thermal expansion coefficient of the ductile cast iron is decreased with the addition of B and P, and is lowest in heat 5(0.04%B and 0.4%P).