Shortening waiting times is the most obvious and effective method of increasing service quality. As the workforce is limited, it is necessary to reform current systems of medical care and improve the efficiency of medical care. After process reengineering was proposed in 1990s, however, this concept has not yet been commonly applied to medical centers. The subject of this study was an outpatient pharmacy in a medical center. This study applied the methods of a time study to measure field observations and as an analytic tool in process reengineering. The results show that the pharmacists were hindered in filling prescriptions for the following reasons: the preparation of certain prescription units, the menial sorting of medicines and also storage issues related to medicines. Improving the process will decrease time wasted by 10.41% and enhance service by 8.95%. The reengineering process resulted not only in a reduction in outpatients' waiting time but also enhanced the quality and competitiveness of the Hospital's medical treatment.