“Tuan Guru Nik Aziz passed away at 9.40pm earlier.
“May his soul be blessed by Allah and place among those who are pious in Heaven,” PAS said in a short statement on their official Facebook page.
The PAS spiritual leader, who suffered from prostate cancer, was admitted in January after his health deteriorated during the recent floods.
Nik Aziz led the Kelantan PAS government for 23 years until 2013, when he stepped down from office and was succeeded by Datuk Ahmad Yaakob.
The veteran Islamist party leader remains popular even among non-Muslim supporters of federal opposition Pakatan Rakyat.
He turned 84 on January 10.