Presenting Author details:naya22@neuroimage.snu.ac.kr Department of Psychiatry, Seoul National University College of Medicine, 28 Yongon-dong, Chongno-gu, 110-744 Seoul, Republic of Korea, Tel.: +82 2 2072 1761; fax: +82 2 766 1685. Background: Although a deficit in social cognition is regarded as an early indicator of schizophrenia, few studies have investigated social cognition in ultra high risk (UHR) individuals for psychosis. The present study was designed to investigate the Theory of Mind (ToM) ability in a UHR group compared to that in a healthy control (HC) group. Methods: Our investigation involved subjects at UHR for psychosis (N=33), age and IQ matched HC group (N=36). Three types of theory of mind (ToM) tasks including the False Belief (FB) task, the Strange Stories task and the nonverbal Cartoon task were administrated to assess ToM mind-reading skill. Furthermore, neuropsychological test battery was measured to consider the possible influence of other components of cognitive function such as memory, language, and executive function on ToM ability. Results: Compared to the HC group, the UHR group performed significantly worse for ToM tasks, with the effect size at an intermediate level (0.57–0.74). Furthermore, the UHR group showed impaired performance in the executive and working memory tests, but not verbal memory tests. The deficits for ToM tasks observed in the UHR group were significantly correlated with set-shifting tasks. Conclusions: Deficits in ToM capability may be modest at the prodromal stage of schizophrenia and may be attributed to prefrontal dysfunction. To prevent or delay transition to psychosis, there is a need for specific preventive strategies targeting social functioning for the UHR group.