The sit-in of around 20,000 people of Tehran in July and August 1906 in UK Embassy is a highly debated issue in the history of constitutionalism. Lasting for a month, the sit-in came to an end after issuance of Constitutional Order by Mozaffar al-Din Shah of Qajar. There is no consensus on the name(s) of organizer(s) and decision-maker(s) behind the sit-in plan, although the role played by  Ayatollah Seyyed Abdollah Behbahani, a prominent Shia cleric and one of the leaders of Constitutional Movement, is worthy of deliberation. This paper intends to shed light on Ayatollah Seyyed Abdollah Behbahani’s role in organizing sit-in in UK Embassy through reviewing opinions for and against the move. An outstanding character opposing the sit-in was Ahmad Kasravi, whose opinion was endorsed by Imam Khomeini. Findings, came through review of various sources and documents on the move and opinions of the historians and researchers, indicate that the sit-in was a recommendation by Ayatollah Seyyed Abdollah Behbahani to a limited number of merchants for their safety and security and it was not a public call for sit-in in the UK Embassy. However, the recommendation found extensive dimensions, apparently contrary to what the ayatollah meant at the beginning, but the roles and influence of his followers and key figures in his house must not be ignored to that effect.