This paper examines Korean learners’ difficulties with English unaccusative verb acquisition. 41 high school students, comprising the low proficiency group and 50 university students, constituting the high proficiency group, participated in judging two kinds of grammaticality tests (context-given and context-free). The first results revealed that at their English proficiency levels, context did not make any difference in judging the grammaticality of unaccusative verb. The second results showed that both groups of learners had more difficulty in acquiring melt-type (unaccusative verbs with transitive counterparts) than die-type (unaccusative verbs without transitive counterparts), and had the most difficulty unlearning NP-be+Ven structure of melt-type, followed by NP-V-NP structure of die-type and NP-be+Ven structure of die-type. It is suggested that the results of this study can be applied to learning and teaching unaccusative verbs in English classrooms and that future research focus on the possibility of advanced learners’ accepting nativelike NP-V order of unaccusative verbs.