University external accountability is institution's commitment and responsiveness for meeting the legitimate demands and interests of the external stakeholders and reporting to them the results and achievements. Proper external accountability can result in confidence, legitimacy, participation and support of stakeholders and play a key role in the university's excellency. Accordingly, the purpose of this article was to assess the external accountability gap within public mother universities of Tehran. A descriptive and analytical survey was conducted through a researcher-made questionnaire. The sample included 350 randomly selected faculty members, university researchers and doctoral students in 3 public mother universities in Tehran, consisting of Tehran University, Shahid Beheshti University and Sharif University of Technology. Data analysis indicated that from academic society point of view the accountability of the public universities to their external key stakeholders is weak and there is meaningful gap between the real and ideal of these universities' accountability situations. The highest level of this gap is seen in accountability of the universities to the labor market, academic society and civil society respectively. However, the accountability to the government is assessed beyond the expectation. Consequently, the public universities should make effective efforts to bridge accountability gap to the labor market, academic society and civil society. On the other hand, reduce their excessive dependence on the government by adoption of effective practical policies and measures.