The main purpose of this research is to explore the key factors contributing to the efficiency operation of the medical information system. In order to identify the related factors influencing user attitude and satisfaction of the medical information-related computer operation in hospitals, 6 general hospitals in Daejeon area were selected and investigated. The scale of hospital were divided into the three groups as the number of beds; A(under 200), B(from 300 to 500), and C(over 600). 291 employees from 6 hospitals were surveyed using questionnaires from July 10 to August 10, 2001. All the data were analyzed by SAS package program. Major findings are as in the follwings. The computer operaters of A group were less educated to information system than the other groups. but they communicated better about the operation of medical information-related computer than the other groups. Onthe other hand, the computer operators from the C group had better skill in the accessibility of necessary information. Factors influencing operator attitude were the inter-connection of information with other departments, accuracy of data collection, and velocity of data handling process. Onthe other hand, factors influencing operator satisfaction were the level of communication regarding information requirement, practice of computer education, and evaluation of computerization. In conclusion, in order to increase computer operation which is the most important success factor, the effort such as operator participation, education, connction of information, and evaluation should be made.