Abstract: The goal of this research was to identify the factors affecting scientists’ adoption of open access publishing and to examine the extent to which these factors influenced the adoption. As an innovative way to disseminate scholarly information, open access journals offer many benefits that would have been impossible in traditional scholarly journals. Despite the increasing popularity, research-oriented publications have been few on the topic of open access, and there has been a lack of understanding of the adoption of open access publishing, which is becoming a hindrance to effective promotion and evaluation of open access journals. Drawing upon Everette Rogers’ diffusion of innovation theory and Icek Ajzen’s theory of planned behavior, this research examined (1) the factors influencing scientists’ intention to publish in open access journals, (2) the measurement scale for each factor, and (3) the relative importance of these factors. To ensure the reliability and validity of survey instrument, this research conducted an elicitation study that comprised pilot interviews, content analysis, operationalization, and evaluation of initial items. A total of 1,104 scientists responded to a Web-based survey. The data analysis identified eleven factors and found that six attitudinal, two perceived control factors and one demographic factor out of the eleven significantly influenced the intention of open access publishing. The social influence and perceived topical compatibility factors appeared to be insignificant for the adoption. The influence of these factors, however, varied among the groups with different tenure status. Prior experience with and knowledge of open access publishing was a significant factor to motivate scientists to adopt open access publishing in general, but the perceived benefit of being visible was considered more important by tenured scientists than by untenured and not-applicable scientists. The untenured and not-applicable groups perceived the benefits of career matters as a more important factor. The findings of this research contribute to our understanding of scientists’ perceptions of and behavior in adopting open access publishing as well as of the measurement scales. Open access publishers and research libraries may also use the results as guidelines in promoting open access publishing and evaluating open access journals respectively.