The purpose of this research is to suggest a model for hospital process and verily the model through analyzing the results before and after reengineering grounded on the activity -based costing. The summary of research is as follows: First, two reengineering-applicable processes for a case hospital are chosen based on the issues from the patient requirements analysis and current process analysis as well as the general characteristics of hospital operations: accounting and clinical laboratory e xami nation processes. The integration of payment-related functions principle is applied to an accounting process which includes three sub processes. while the automatic transition of laboratory output principle is applied to a clinical laboratory examination process. Second, the studs shows more than 50% reduction of activities: nine activities from nineteen by the principle of integration of payment-related functions, and nine activities from fourteen by the principle of automatic transition of laboratory output. Finally. activity-based cost analysis before and alter reengineering results in 44% cost reduction: 43.9% in payment-related subprocesses and 41.1% in a clinical laboratory examination process. Therefor this research finds an enormous gap between costs before and after reengineerring. The contributions of this research are two-fold: one is that activity-based costing methodology is practically valid for measuring the cost-performance analysis of hospital process reengineering, and another is that activity -based costing can he utilized not only an initiative of process engineering hut also as a tool for evaluating a variety of activities by a simulation technique.