The 42-year-old had been arrested at an address in Leeds on Tuesday night on suspicion of arson.
It follows fires started at the front doors of the Jamia Masjid Abu Huraira Mosque in Hardy Street, Beeston, and the Guru Nanak Nishkam Sewak Jatha Gurdwara, in Lady Pit Lane, in the early hours of Tuesday.
A police spokesman today said that the man had been released under investigation as enquiries continue.
Read more: Mosque and Sikh temple in Leeds set on fire in arson attacks on the same nightDetectives still want to hear from anyone who witnessed anything suspicious at either location or who saw any person or vehicles near the places of worship between 3am and 4am on Tuesday.
Anyone with information is asked to contact Leeds District CID via 101 quoting crime reference 1318270739 or call the independent charity Crimestoppers anonymously on 0800 555 111.