This study examined how the different grammar instruction affect the acquisition of English relative pronouns of Korean EFL learners specifically focusing on low-level students. One hundred and four university students with low English proficiency level were participated in the study and assigned to the either deductive or the inductive grammar instruction groups. The participants English grammar acquisition was checked through pre, post, and delayed tests. The results revealed that both of the instructions positively influenced on the learners grammar acquisition for the long-term retention even though the learners in the deductive instruction group initially showed greater improvement in their L2 grammar knowledge.