The purpose of this study is to examine a possibility of applying the ABC system to analyze the cost of nursing service on one obstetrics and gynecology (OB/GYN) unit in a major medical center. The activities of nurses on an OB/GYN unit were analyzed for 4 days for 96 hours. 2 week days and 2 days on weekend. Total cases included in the study were activities of 12 charge nurses and 12 staff nurses. Activities were categorized into direct and indirect activities in order to calculate the cost of activities. Nursing activities were defined multidimesionally in order to utilize the ABC system. The 60 nursing activities were classified into the direct nursing activities and the indirect nursing activities based on a literature review, interview, and survey results. The direct activities were further categorized into the single nursing activities and the multiple nursing activities. The indirect activities were classified into the indirect nursing service activities and the general management activities. The major findings of this study were as follows : 1. There were differences in activities according to the positions and duties of the nurses. The charge nurses mostly performed the indirect nursing service activities and the general management activities. Almost all of their indirect nursing activities spent on each patient were similar. The staff nurses performed the single nursing activities and the multiple nursing activities. 2. The activities of staff nurses included medication, patient assessment, rounding and organizing the unit. patient education, nursing treatment, admission and discharging of patients. There was no differences in types and amount of time spent between the nurses on day-time duty and evening-time duty, but the patient assessment activity increased during the night-time. 3. The cost of post partum nursing services for women who had a normal vaginal delivery using the ABC system included the cost incurred by direct nursing activities provided by the staff nurses (85.9%), indirect nursing activities incurred by the staff nurses(19.0%) and the nursing activities by the charge nurses and the head nurse(14.1%). The ABC system is a relatively new method of cost analysis. The results of this study can provide the nursing and hospital managers with useful information on cost control. It is suggested that more studies should be done using the ABC system and extend the scope of studies to include value analysis to aid the Activity-Based Management(ABM) and/or the reengineering of hospital process.