With the development of internet technology, people can share knowledge through Q&A websites anytime and anywhere. However, two types of barriers between the questioners and respondents make knowledge sharing difficult: 1) lack of trust for other users, 2) an arrogant or negative attitude exhibited by the questioners. We conducted an experiment to evaluate the effect of the virtual agent for lowing these barriers with two characteristics: 1) similar profile to users, good appearance and affable personality for users, 2) positive attitude and reaction. The results indicate that the virtual agent can improve the users’ motivation to answer questions.