Continuing professional education is essential for nurses to update their clinical skills and knowledge to meet the complex demands of current patient care. Compared to traditional in-class continuing education, a web-based learning system is efficient for nurses with a three shift-working schedule and is timely to deliver knowledge about newly emerging epidemics such as Severe Acute Respiratory Syndrome. Many studies reveal the advantages of various web-based learning systems but seldom evaluate them from the perspective of quality. This study develops an instrument to assess the quality of a web-based learning system for nurses' continuing education based on the quality dimensions of a mature information systems success model. The research results show that all indicators of the instrument provide a fit to the quality measurement of a web-based learning system and have high reliability and validity. Based on the research findings, implications and limitations are discussed.