The military rank of Margaret Houlihan on M*A*S*H was major. Known by the nickname “Hot Lips,” Major Margaret Houlihan served as the head nurse of the fictional 4077th Mobile Army Surgical Hospital during the Korean War.
Houlihan appeared in the original novel, the 1970 film, and the television series. Sally Kellerman played her in the film, while Loretta Swit portrayed her on television. The character initially aligned herself with Major Frank Burns and often clashed with the unit’s irreverent surgeons, but the series gradually developed her into a more sympathetic and independently minded officer.
Her rank is sometimes discussed by fans because the show’s timeline and her stated years of service do not always align perfectly with historical promotion expectations. That continuity issue does not change the answer: throughout the central M*A*S*H setting, Houlihan is identified as a major. She later receives a promotion to lieutenant colonel near the series’ conclusion.