As the rapid development of open source software (OSS) has deeply impacted global software industry, government agencies in different countries all over the world have started to realize the huge potentials of OSS application. Based on the TOE framework for organizational level IT/IS adoption, this paper proposes a conceptual model for examining the adoption of open source software in the governmental organizational context. A positivistic case study is conducted in the government agencies of Beijing, China, so as to validate and develop the proposed model, as well as to investigate the adoption status and related influence mechanisms. Findings from the analysis demonstrate the explanatory validity of the model, and provide potentially helpful insights for future practice.