There have been many studies on the acquisition of English unaccusative verbs which make use of learner corpora. Most of these studies have so far concluded that even advanced learners of English ungrammatically passivize unaccusative verbs and produce sentences such as "*The accident was happened" and "*The mobile phone was appeared." These ungrammatical passives thus produced are referred to as "passive unaccusatives" by many researchers. Oshita (2000) is probably the first to analyze examples of these ungrammatical unaccusative passives in a written learner corpus. He used data from Japanese learners consisting of 1,363 essays from the Longman Learners Corpus (LLC). However, in order to gain a more thorough understanding of Japanese learners of English, a corpus of 6,161 essays written by Japanese learners of English is used in this study. The findings in this study are that (1) Japanese learners of English do in fact produce ungrammatical unaccusative passive uses of "appear," "happen," and "occur" in writing; (2) they tend to use "appear," "happen," and "occur" with adverbials; and (3) while they sometimes use "happen" and "occur" as causative verbs, they do not use "appear" in this way.