This study extends the application of Social Cognitive Theory (SCT) to investigate the nature of Weibo posting anxiety and its determinants (i.e., micro-blogging self-efficacy, outcome expectations, and prior experience) among well-educated youth in China. Analyzing semi-structured interviews with Chinese Weibo users, this study identified four dimensions of microblogging posting anxiety, including social-, writing-, technology-, and safety-related anxiety. Fear of receiving negative evaluation from offline friends and leaking personal information to unknown/dangerous readers were the main reasons for their Weibo posting anxiety. Prior experiences of obtaining undesirable comments and disappointing feedback were found to create negative outcome expectations of Weibo usage (e.g., deteriorating self-presentation and causing misunderstanding), which may indirectly induce Weibo posting anxiety. However, self-efficacy did not play a significant role in generating anxious reactions towards Weibo posting. Theoretically, this study uses an SCT analytical lens to enhance the understanding of Weibo posting anxiety among Chinese users. Practically, the findings provide insights to services operators and system designers about users’ anxiety in using social media like Weibo so as to improve the service and boost the usage. Note: An oral presentation of this article was made at the 2014 annual meeting of the Association for Education in Journalism and Mass Communication (AEJMC), Montreal, Canada.