Based on TPB model, the paper proposes an extended model to explain the intentions of potential respondents' to participate in Web-based surveys. The chief objective of this paper is to obtain a more comprehensible picture of how intentions are formed. We empirically tested the research model with a sample 131 participants. Hierarchical regression and structural equation modeling were used and the results indicate that attitude of potential respondents, social norm, perceived behavioral control and PWI are determinants of unit nonresponse in Web-based surveys. The results testify the usefulness of TPB model to explain the intention of potential respondents to take part in Web-based surveys and on the other hand, the results also verify the importance role of the PWI in web-based survey.