Objective: This study was conducted to clarify influential factor and structures of Clinical Competency (CC) at psychiatric nurses. Method: A mail questionnaire survey was administered to psychiatric nurses in Japan. The questionnaire consisted of CC and influential items and basic attributes inferred from categories obtained from a comparative analysis of behavior event interviews. Results: The questionnaire was distributed to 9,369 nurses, from whom 6,147 (65.6%) responses were collected, of which 5,107 (83.1%) represented valid responses. Factor analysis yielded four CC factors and five influencing factors. Results of a covariance structure analysis revealed that the CC of psychiatric nurses comprised four independent factors, "assessment," "helping practice," "creating a basis for helping," and "use of knowledge from experience," with 12 nursing activities representing the factors. Additionally, CC was found to be influenced by [efforts to improve the nursing competency] expressed in < looking for clues to success >, <useful consciousness of training>, <learning from seniors>, <support systems for growth>, and <useful experience of basic education> (GFI 0.961, AGFI 0.952, RMSEA 0.041).