The present invention provides an ester plasticizer for polyvinyl chloride (PVC) resin, epoxy resin or urethane resin and a method of preparing the same. More particularly, the present invention provides an ester plasticizer using triacetin and coconut oil-based biodiesel as raw materials, which can prepare a resin composition having excellent plasticizing efficiency and improved physical properties such as tensile strength and the like. When a polyvinyl chloride resin or the like is manufactured using the ester plasticizer, there are advantages in that an environment-friendly product having an excellent plasticizing efficiency and in that the physical properties such as hardness, tensile strength, etc. of the product are improved.