Suh, Jae-Suk. 2000. A Difficulty Ordering for the Learning of English Relative Clauses. The Journal of English Grammar 4.1, 5-22. This paper examined the learning of four types of relative clauses by Korean and Japanese learners of ESL. The four types of relative clauses were: SS, SO, OO, and OS (the first character of each type stands for the role of the identical noun phrase in the main clause while the second one represents the role of the identical noun phrase in the relative clause). Subjects were two Korean and two Japanese learners of ESL, who were in intermediate proficiency level. Data were collected via sentence combining and elicited imitation tasks. The findings of the study showed that 1) OO and OS types were produced more accurately than SO and SS types; 2) The learners showed a strong preference for OS type over SO in their production; and 3) The learners comprehended better on OS and OO types than SS and SO types. As a possible explanation for these results, since the SO and SS types are sentences interrupted by relative clauses in the middle of the sentence whereas the OO and OS types are not, it is highly likely that such embedded clauses become an obstacle to the processing of a whole sentence for both Korean and Japanese learners whose native languages do not have center embedding in relative clause constructions. Based on the findings, a difficulty ordering of the four types of relative clauses was proposed: (least difficult) OS > OO > SS > SO (most difficult). (Korea University)