The trial focuses on events at the Akinci airbase which it is alleged was the plotters' headquarters.
It is taking place in a purpose-built courtroom outside the capital Ankara.
The defendants face charges from attempting to assassinate the president to murder. As some arrived at court they were met by protesters chanting "We want the death penalty!"
Some of the demonstrators had relatives killed or injured during the coup attempt and threw nooses towards the suspects.
Rebel soldiers tried to grab power in July 2016, leaving 249 civilians dead.
Military chief Gen Hulusi Akar and other senior officers were held hostage at the base for several hours on the night that the coup took place.
The trial is the largest yet relating to the coup. Anyone convicted is expected to get life imprisonment.
Although Turkey abolished the death penalty in 2004, President Recep Tayyip Erdogan proposed a referendum on the issue in his speech after narrowly winning a vote to expand his powers in April.
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