Demands for the death of a newspaper editor who was improperly respectful of the Prophet:
Oh judges of the Sudan, defend the honour of the Prophet," read one banner.
"The court must execute him - this is an insult not to any ordinary man - this is an insult to a prophet," one man said.
The protesters made speeches through loudspeakers and handed out statements, demanding that the authorities hand Mr Taha over so they could kill him.
Mr Taha is a prominent Islamist journalist and has close ties to the Muslim Brotherhood political group.
He has not yet commented on the allegations against him but a journalist from his newspaper said it was a "big misunderstanding".
Those who renounce Islam face the death penalty in Sudan.
Ali Shumi, the head of Sudan's Press Council, said the article insulted the Prophet Muhammad.
Let me repeat one line : Those who renounce Islam face the death penalty in Sudan.
The article goes on to explain that freedom of the press doesn't mean you can say what you want about religion.