This paper identifies two types of 'uy', which has been called an adnominal particle in Korean, and presents a syntactic analysis of them. The particle 'uy' can be divided into two types; genitive marker 'uy' and modificational marker 'uy'. The former, realized as structural Case, attaches to an argument noun phrase of referential semantic type. In contrast, the latter has a function of attributive modification, whereby combined with a non-argument noun phrase of property semantic type. Genitive marker 'uy' is licensed at the Spec of DP position, whereas modificational marker 'uy' occupies an NP-adjunction position. This paper also discusses so-called compound nouns, in which 'uy' is not allowed to intervene. Those constructions are shown to have properties as syntactic products and to have type interpretations of head nouns.