Acquisition of relative clauses in Korean and Japanese has been one of the fruitful research topics in the modern linguistics. Kim (1987) and Lee (1991) especially have revealed many interesting aspects of the acquisition of relative clauses, especially the relative clauses in Korean. They claim that so-called externally-headed relative clause constructions are acquired earlier than the internally-headed relative clauses in Korean. Contrary to what Kim (1987) and Lee (1991) claim, Cho (1999, 2003) proposes an alternative such that the internally-head relative clauses (IHRCs) in Korean are acquired earlier than the externally-headed ones (EHRCs). If this is the case, then why? Cho (2003) simply remarks that children tend to acquire structures that are easy to understand earlier than those that are not. We will critically re-examine this claim and provide some explanation. That is, we show that IHRCs are acquired earlier than EHRCs because the former are semantically more transparent than the latter, while having the same syntactic structures.