This research examines the possessor raising construction as an example of optional case marking in Korean from the perspective of optimality theory. Traditionally, the main function of the case markers is to indicate the grammatical relation of the NP in a clause. So, the relationship between the case marker and the grammatical relation is mainly regarded as one-to-one mapping. However, this research claims that the interaction between the grammatical relation and information status of the NP provides the proper form of case marking for the possessor.