Hao or HAO may refer to:
- Hào, a form of Chinese pseudonym
- Hao (Chinese surname) (郝), a Chinese surname
- Hao (French Polynesia)
- Hao (city), (镐/鎬, an abbreviation for the city of Xi'an, Shaanxi (China)
- Haojing, (镐京/鎬京) ancient capital of the Zhou Dynasty which stood on the spot of present day Xian
- Hao Mengling, Chinese general
- Hao Asakura, a character in Shaman King media
- Hao Si-wen, a character in the Water Margin universe
- Hsu Hao, a character in Mortal Kombat media
- HAO or High Altitude Observatory
- HA0, a postcode area of the United Kingdom
- Hao of Oahu, Prince of Oahu
- Heather O'Reilly, Heather Ann O'Reilly, American soccer player.
- Rauvolfia sandwicensis, a plant endemic to Hawaii