The present study examines the validity of Hamilton hypothesis in English relative clause (RC) production. Hamilton (1995) argues that English as a second language (ESL) learners may be sensitive to the difference of configuration rather than that of grammatical relation in English relativization. Twenty item RC test was administered to Japanese learners of English (N=100). The test consists of four parts: (1) argument/ object of preposition; (2) adjunct/ object of preposition; (3) argument/ indirect object; and (4) argument/ object of preposition. The difference between (1) and (2) is configuration (argument vs. adjunct) and (3) and (4) grammatical relation (indirect object vs. object of preposition). The results indicate that Japanese learners of English are more sensitive to configuration than grammatical relation. The criticism of recent treatment of Noun Phrase Accessibility Hierarchy and implications of the research findings for language testing and second language acquisition research methodology are also discussed.