Japan has the largest number of psychiatric beds per population in the world. At the same time, little research had been done to describe nursing care delivered in psychiatric units. To describe contents of nursing care, the framework for care classification and measuring methods must be examined. The purpose of this study was to develop a nursing intervention classification and examine the correlation between amount of care and patients' mental states. Data were collected from 39 patient care records from 4 randomly selected psychiatric hospitals. Patients' function and condition were evaluated by their doctors using the Global Assessment of Functioning (GAF) and the Brief Psychiatric Rating Scale (BPRS). Six care categories were extracted: basic activities of daily living, psychological support/interpersonal skills, medical support, monitoring, family support and miscellaneous. By examining three cases with this classification, there were significant correlations between the GAF and BPRS scores and amount of care for two acutely ill psychotic patients.