Maechi or Mae chee (Thai: แม่ชี; IPA: [mɛ̂ː.t͡ɕʰiː]) are Buddhist monastics in Thailand who have dedicated their life to religion, vowing celibacy, living an ascetic life and taking the Eight or Ten Precepts (i.e., more than the Five Precepts taken by laypersons). They occupy a position similar to sāmaṇerī.

It is still illegal for women to take full ordination as a bhikkhuni (nun) in Thailand because of a 1928 law created by the Supreme Patriarch of Thailand. He based this on the belief that Gautama Buddha allowed senior bhikkhunis to initiate new women into the order. Citing the belief that the Theravada bhikkhuni sangha had died out centuries earlier and the Buddha's rules regarding bhikkhunī ordinations according to the Vinaya, the patriarch commanded that any Thai bhikkhu who ordained a female "is said to conduct what the Buddha has not prescribed, to revoke what the Buddha has laid down, and to be an enemy of the holy Religion...". The most recent case brought to the Supreme Court of Thailand is that of Phothirak, a former monk who has been ejected from the Thai sangha after being convicted of breaching the vinaya repeatedly. Phothirak then created his own sect of Buddhism, Santi Asoke, and ordained about 80 bhikkhunis in 1998, leading to his imprisonment for 66 months on several successive counts of "causing schism amongst the religion".

Maechis have traditionally been and still are marginalized figures in Thai society. During the 20th century, new movements to improve the lot of maechis emerged. But the situation is still far from being acceptable under modern standards of human rights, with other Thai women often the most vocally opposed to women wearing robes. The Thai bhikkhuni order has been revived by Dhammananda Bhikkhuni, who took ordination in a reestablished bhikkhuni lineage in Sri Lanka without being imprisoned as a result. But opposition from high-ranking Thai monks seems to have discouraged maechis from joining her. Since 1971 there has been a Queen's Foundation for Thai Maechi, addressing maechi affairs.