This study examines how Keenan and Comrie's (1977) noun phrase accessibility hierarchy (NPAH) intersects with the typological characteristics of Korean in the acquisition of relative clauses (RCs). Korean has two types of RC constructions: head-external and head-internal. The head-external relative has its head to the right of the RC, whereas the head-internal relative has its lexical head in the RC and is marked by the complementizer "kes." In first language development, it has been observed the head-internal type emerges earlier than the head-external type. The current study investigates how the use of the two types of RCs interacts with the NPAH, with a focus on subject (SU) and direct object (DO) RCs in Korean second language development. Oral production data were collected from 40 learners of Korean as a foreign language. The results showed that there was an advantage for SU over DO in the head-external RC and that the head-external construction was preceded by headless and head-internal constructions. The results suggest that a head-external RC in Korean involves the syntactic mechanism of linking the head and the gap relation, whereas this might not be the case for a head-internal RC.