This study aims to examine the work ethic of Islam, affective commitment and altruism on knowledge sharing behavior. In this study, the respondents who are working in other organizations or institutions. They are also studying at the Master of Management in 5 universities in the Special Region of Yogyakarta. The researcher obtained 130 respondents. This research used purposive sampling technique. In addition, this research also used Structural Equation Modeling analysis techniques with AMOS as an analytical tools. In this study has results of data testing obtained that: 1) Islamic work ethics has a positive and significant impact on altruism. 2) affective commitment has a positive and significant effect on altruism. 3) Islamic work ethics has a positive and significant impact on knowledge shring behavior. 4) affective commitment has no positive and significant effect on knowledge sharing behavior. 5) altruism has a positive and significant effect on knowledge sharing behavior. Keyword: Islamic work ethics, affective commitment, altruism, knowledge sharing behavior