The present study examines the learnability problem experienced by Japanese-speaking learners in L2 acquisition of English psychological (psych) verbs. The main purpose of the study is to investigate whether Japanese learners know the properties of English Object Experiencer (OE) verbs, which previous studies have also reported as being problematic for learners. An experimental study was conducted to investigate this issue, in which two groups of learners (advanced and intermediate) and one group of English native speakers (control) participated. An English OE verb was presented in two different types of adnominal clauses: "-ed adjectives" and "-ing adjectives", combined with two types of arguments (Experiencer/Theme), respectively. The results revealed that the Japanese learners are not aware of the different properties between English OE verbs and Japanese Subject Experiencer (SE) verbs. A possible explanation for the results is discussed relating the difference between English and Japanese psych verbs.