The Korean 3rd person pronoun ku, along with kunye, is treated as an exotic element in Korean since they are very different from other 3rd person pronouns in their forms and usages. In fact, one might be reluctant to include them in the Korean pronominal system due to their heterogeneity. However, since those pronouns have stable usages and an established status especially in written Korean, it is very desirable to clarify their nature. On the other hand, English pronouns have been regarded as belonging to the category of determiner in the tradition of generative grammar. Thus, expressions like we Americans are taken to have a structure parallel to the Americans. It we follow this tradition of generative grammar in analyzing pronouns as determiners, we seem to have to treat Korean pronouns as being included in the category of determiner. However, as it is problematic in many ways to treat them as determiners, it is an important task in Korean syntax to clarify their nautre. In this respect, this study tries to determine what the categorial status of ku in the framework of generative grammar, and what is the implication its categorial status has with respect to the Korean noun phrase structure.