Mannhai is a Finnish stoner rock band from Helsinki. The band was formed in late 1999 by bass player Olli-Pekka "Oppu" Laine and guitarist Ilkka "Ile" Laaksomaa. Soon they were accompanied by a young drummer, Mikko "Junior" Pietinen, and the following year by lead singer Jani "Joãnitor" Muurinen.

In 2004, Muurinen left the band after three albums. In 2005 Mannhai persuaded Pasi Koskinen to replace Muurinen as a vocalist. Koskinen is best known for being the lead singer of Amorphis during the years 1996–2004.

The band's name Mannhai comes from an Indian belief. In the countryside of the state of Uttar Pradesh in India, people in villages believed an evil disguised spirit called the Mannhai snatched their children at nightfall.