The purpose of this study is to evaluate the effects of the Great Hanshin Earthquake in January 1995 on the onset of symptoms of the Posttraumatic Stress Disorder (PTSD) and psychological stress responses systematically. Three to four months after the quake, one hundred twenty eight earthquake victims (males : n-62,Age : Mean : =34.89±12.51,Min.=18,Max.=73; females : n=66,Age : Mean=29.56±11.42,Min.= 19,Max.= 62) were requested to complete a questionnaire, which consists of items from DSM-IV diagnostic criteria for PTSD and Psychological Stress Response Scale (PSRS-18). The rate of. prevalence of PTSD was 12.90% for males, 9.09% for females, and 10.94% for total subjects, suggesting that the prevalence rate of PTSD is almost same as one described in DSM-IV. Victims showed symptoms included DSM-IV criteria category B (persistent reexperience of traumatic events) most frequently (92.97%), followed by category D symptoms (persistent increased arousal : 54.69%), category F symptoms (distress or impairment of social and occupational functioning : 28-91%), and category C symptoms (persistent avoidance of trigger and numbing of responsiveness : 25.00%). Among category B symptoms, 82.03% of victims showed intense psychological distress at exposure to triggers, 69.53% of them showed recurrent and intrusive recollections of the traumatic event and acting or feeling as if the traumatic event were recurring, whereas only 15.63% of victims showed psychological reactivity on exposure to triggers. Among category C symptoms, efforts to avoid activities., places, or people that arouse recollections of the trauma was found in 69.53% of victims and sense of foreshortened future was found in 37.50% of victims. As there were no differences in the occurrence of category D symptoms, 35% to 50% of victims showed each symptom. Regarding to the results of PSRS-18,comparison of PSRS-18 scores between victims and the normative data revealed that victims showed significantly higher scores in all subscales : Depressive-anxious mood, Irritability and anger, and Helplessness. No significant gender difference was found. Further analysis of PSRS-18 scores revealed that victims with PTSD symptoms showed significantly more psychological stress responses than victims without PTSD symptoms in all subscales. These results were discussed with reference to past research data on PTSD caused by quake disaster. The importance of social support system to reduce psychological stress responses and some implications for the intervention of PTSD were discussed.