This study tries to uncover the relationships of factors influencing the intention and the behavior of health knowledge sharing on the Internet under the Web 2.0 environment based on Theory of Reasoned Action (TRA), intrinsic motivation, and Technology Acceptance Model (TAM). To this end, factors reflecting personal characteristics (i.e., attitude, subjective norm, self-efficacy, and enjoyment of help) and factors reflecting system characteristics (i.e., perceived usefulness, perceived ease of use) are selected as variables of the intention and the behavior of health knowledge sharing on the Internet. In this study, the research model was tested by using structural equation modeling approach was used to analyze collected data. Results of the study show that factors such as subjective norm, enjoyment of help, and perceived usefulness are significantly associated with intention and behaviors of sharing health knowledge on the internet. However, the results reveal that attitude, self-efficacy, and perceived ease of use do not affect the intention and the behavior of sharing health knowledge on the internet.