The Department of Clinical Laboratory, Nagoya University Hospital acquired ISO 15189 accreditation in November, 2009. The operation of our Quality Management System (QMS) was first surveyed in October, 2010. In this paper, we reported the activity for the preparation and operation of our QMS and the effects of ISO 15189 accreditation. We investigated the changes in the number and content on nonconformities, incident reports and complaints before and after accreditation as indicators to evaluate the effect of ISO 15189 accreditation. Post accreditation, the number of nonconformities and incident reports decreased, seeming to show an improvement of quality of the laboratory activity; however, the number of complaints increased. We identified the increase of complaints at the phlebotomy station. There had been some problems with blood sampling in the past, but it seemed that staff had a high level of concern regarding these problems at the phlebotomy station and took appropriate measures to resolve the complaints. We confirmed that the ISO 15189 accreditation was instrumental in the improvements of the safety and efficiency on laboratory works. However there was a problem that increase of overtime works to operate the QMS. We deal with development of a laboratory management system using IT recourses to solve the problem.