Some 100 human rights activists, including artists and journalists, gathered outside the courthouse in support of the artist who has played with the philharmonic orchestras of Berlin, New York, Tokyo and Israel.
“Fazil Say is not alone,” read one of the banners held by the peaceful protestors.
The virtuoso, 42, is charged with inciting religious hatred and insulting Islamic values in a series of provocative tweets.
He faces up to 18 months in prison if convicted.
The case has revived fears of increasing restrictions on freedom of speech in Turkey and concerns that the secular country was becoming more Islamist.
Say said he was “amazed” by having to appear before judges in a note he sent to a gathering of fellow artists on Tuesday to show solidarity with the acclaimed composer.
“All my life, I have represented the modern face of Turkey to the world through my art..I feel weird because I am facing the threat of being punished with a case like this,” he said.
The indictment cited some of his controversial tweets from April, including one where he said “I am not sure if you have also realized it, but all the pricks, low-lives, buffoons, thieves, jesters, they are all Allahists.”
Say was also the target of public outrage when he posted tweets denouncing what he branded the hypocrisy of the pious in Turkey.