Seyyed Hassan Modarres (Persian: سید حسن مدرس ‎) (c. 1870 - December 1, 1937), was an Iranian Twelver Shi'a cleric and a notable supporter of the Iranian Constitutional Revolution. He was among the founding members, along with Abdolhossein Teymourtash, of the reformist party Hezb-e Eslaah-talab of the time, which was formed during the fourth national Majlis of Iran. He has been called "brave and incorruptible" and "perhaps the most fervent mullah supporter of true constitutional government."

The sources disagree on his birthplace. Some mention that he was born in Shahreza, while others mention that he was born in a village named Sarābe-Kachou (سرابه‌کچو) near Ardestan, and that he moved to Shahreza when he was six. Having studied Islamic sciences in Isfahan and Najaf, Modarres turned to become a religious teacher in an Esfahan's madrasa. The name Modarres, that means "teacher", is because of his job there. In 1910, he was chosen by Najaf's cleric community and sent to Tehran to supervise the laws passed by the Majlis of Iran, to make sure they are not against the rules of sharia. Later, in 1914, he was elected as a Majlis representative of Tehran.