Mani stones are stone plates, rocks and/or pebbles, inscribed with the six syllabled mantra of Avalokiteshvara (Om mani padme hum, hence the name 'Mani stone'), as a form of prayer in Tibetan Buddhism.

The term Mani stone may also be used in a loose sense to refer to stones on which any mantra or devotional designs (such as ashtamangala) are inscribed. Mani stones are intentionally placed along the roadsides and rivers or placed together to form mounds, cairns or sometimes long walls, as an offering to spirits of place or genius loci.

Creating and carving mani stones as devotional or intentional process art is a traditional sadhana (spiritual practise) of piety to yidam (enlightened being). Mani stones are a form of devotional cintamani (philosopher's stone).