Tianzi may refer to:

• Tianzi Mountain, a mountain in Hunan, China
• Son of Heaven, a title of the Chinese sovereign, rulers of a particular period in ancient China
• Empress Tianzi, a character in the manga/anime Code Geass

• First Army (Ottoman Empire)
• First Army (Russian Empire)
• First Army (Soviet Union)
• First Article Inspection
• First article inspection
• First ascent of the Matterhorn
• First Asia Institute of Technology and Humanities (FAITH)
• First Asian Athletics Championships
• First Assembly Christian School of Concord, NC
• First Assembly of Experts
• First Assembly of God
• First assistant
• First assistant camera
• First Assistant Engineer
• First Assyrian Dynasty
• First Atlanta
• First Australians
• First Automobile Works
• First Automotive Group Corporation
• First Avenue (disambiguation)
• First Avenue School
• First AVNOJ Conference
• First Avon and Somerset
• First Azarov government
• First Badgerline