The competition between hospitals of the same district becomes more intense. In order to consolidate health care market share, it is important to know the medical market and patient characteristics for developing suitable business strategies. With hundreds of hospitals and clinics, Taiwan has an intense medical market competition. Via data mining and cluster analysis with National Health Insurance Research Database (NHIRD), a study on patients' characteristics and treatments of Obstetrics and Gynecology is presented as a reference for Taichung city's hospitals to develop business strategy.