Representatives from 57 OIC members are attending the summit, which is meant to coordinate a response to a US decision to recognize Jerusalem (al-Quds) as Israel’s capital.
Iranian President Hassan Rouhani traveled to Istanbul to take part in the summit.
It follows US President Donald Trump’s controversial recognition of the holy city as the capital of Israel and his decision to move its embassy from Tel Aviv to Quds.
The decision has drawn widespread international condemnation and sparked protests in the Palestinian territories.
The summit also follows Turkish President Recep Tayyip Erdogan’s call on OIC member countries to gather extraordinarily after the US move on the holy Quds.
Erdogan has said that the OIC summit on Wednesday would convey the message that Washington should swiftly reverse its decision.
Israel has occupied East Quds since the 1967 Middle East war. It annexed the area in 1980 and sees it as its exclusive domain. Under international law, the area is considered to be occupied territory.