This corpus-based study investigates syntactic characteristics of English relative clauses used by EFL speakers who are Korean adults and focuses on the grammatical function of gaps and fillers which are claimed to influence the acquisition and use of such clauses. The study reveals that although both Korean EFL speakers and English native speakers prefer to use English relative clauses which are positioned at the ends of sentences, Korean EFL speakers use relative clauses where both gaps and fillers are subjects more frequently than relative clauses where both gaps and fillers are objects or complements. Furthermore, Korean EFL speakers do not use English relative clauses with gaps that function as indirect objects. We claim that the way Korean EFL speakers use English relatives clauses is the result of L1-transfer on the ground that similar patterns of use are found in Korean.