Recently, there has been much interest for knowledge sharing within professional group, especially physicians in hospital. This study investigates the factors affecting physician's knowledge sharing behavior within a hospital department by employing existing theories. The research models under investigation are the theory of reasoned action (TRA) and the theory of planned behavior (TPB). These models are empirically examined and compared based on the survey results on physicians' knowledge sharing behavior collected from 286 physicians practicing in 28 types of subunits in 13 tertiary hospitals in Korea. The TPB model exhibited good fit with the data and appeared to be superior to the TRA in explaining physicians' intention to share knowledge. In the modified TPB model, subjective norms were found to have the strongest total effects on behavioral intentions to share knowledge of physicians through direct and indirect path by attitude. Attitude was found to be the second important factor influencing physicians' intentions. Perceived behavioral control was also found to affect the intention to share knowledge, though in a lesser degree than subjective norms or attitudes. Implications are also discussed for physician's knowledge sharing activities. (C) 2003 Elsevier Science Ltd. All rights reserved.