Mahmut Ustaosmanoğlu (1929 – June 23, 2022), usually referred to as Mahmut Effendi and known to his disciples as "Efendi Hazretleri", was a Turkish Sufi Sheikh and the leader of the influential İsmailağa jamia of the Naqshbandi-Khalidiyya Ṭarīqah centred in Çarşamba, Istanbul.