Purpose: The purpose of the study was to identify critical indicators for the development of efficient patient classification system in a emergency room. Method: This study involved following five steps. Step 1. Selection of the lists direct nursing services in the ER. Step 2. Measurement of the time of direct nursing services from Aug. 31st to Nov. 30th, 2005. Step 3. Classification of the patients according to the nursing care time. Step 4. The determination the critical indicators for different patient classes. Result: Determinate indicators were as follow: 3 items in the first group (vital sign checking, IV route starting, blood sampling), 3 items in the second group (vital sign checking, fluid infusion, blood sampling), 9 items in the third group (I/O checking, $O_{2}$ inhalation, suction, fluid infusion, IV bolus, Central catheter preparation & management, blood sampling, intubation preparation & management, postmortem management), 7 items in the fourth group (EKG monitoring, BP monitoring, $O_{2}$ inhalation, fluid infusion, using the specific drugs, CPR, postmortem management). Conclusion: This study can help future studies which measure nursing services standard time or assigns value to emergency nursing services.