Purpose : The purpose of this study was to identify the Performance frequency of nursing intervention according to domains and classes, and core nursing interventions performed by psychiatric nurses using the 3th NIC. Method : For this purpose, the 3th nursing intervention classification(NIC) was used. In this study a 435 of 486 nursing interventions were selected from 75% consent reached by experts. Data were collected from 9 hospitals and 141 nurses(return rates : 94.0%) in Seoul. Kyonggi, Chungnam, Gwang-ju and Chonnam region from January, 2002 to February, 2002 using 5 point Likert scale. Results : Respondents were mostly female (99.3%), married(53.9%) and college graduate(46.1%). The mean age was 32.34±7.96 age, the mean length of service as a nurse was 111.33±73.67 months and the mean length of service in psychiatric unit was 82.06±66.30 months. The most frequently performed domain was found to be `behavioral` (2.872±0.634), followed by `health care system` (2.804±0.570) and `safety`(2.465±0.522) domain. The most frequently performed class appeared to be `communication enhancement` (3.157±0.699), followed by `information management` (3.153±0.616). `coping assistance` (3.063±0.696), `behavioral therapy`(3.063±0.696) and `risk management`(2.885±0.608) class. And the most frequently performed nursing intervention was `active listening` (4.943±0.261), followed by `documentation`(4.843±0.566), `emotional support`(4.816±0.424), `counseling` (4.649±0.654) and `complex relationship building` (4.603±0.745) nursing intervention. Conclusion : In conclusion, the 3th NIC was found to be a general and comprehensive classification system in application to psychiatric unit. And there were specific nursing interventions performed in the psychiatric unit, which belong to behavioral domain, risk management class and self-care assistance class. Therefore, unique and appropriate nursing interventions in psychiatric unit for Korean nursing environment need to be developed through results using NIC.