Organizational knowledge is regarded as a key source of sustainable competitive advantages for organizations. Along with the development of information technology, organizations often find many ways to facilitate the online knowledge sharing process. However, the establishment of successful online knowledge sharing initiatives seems to be challenging to accomplish. This study aims to enhance the understanding of the factors that affect employees’ knowledge-sharing behavior in organizations by examining the integration of two social psychology models—the Technology Acceptance Model (TAM) and the Theory of Planned Behavior (TPB). A total of 501 complete responses, from full-time employees in Vietnamese tele-communication companies, were collected and used for data analysis using structural equation modelling. The overall findings of this study appear to coincide with the propositions of the TAM and the TPB, which this research model was built on. Perceived ease of use and perceived usefulness significantly affect employees’ attitudes toward knowledge sharing. In turn, attitudes, along with subjective norms and perceived behavior control (PBC), have a positive influence on knowledge sharing intentions (KSI). Consequently, KSI can be used to predict knowledge donating and knowledge collecting.