Lossarnach was a province of Gondor situated to the south-west of Minas Tirith in the south-facing valleys of Mount Mindolluin, the most eastern of the White Mountains. It lay between the rivers Sireth and Erui. The vale of Imloth Melui, known for its wild roses, was situated in Lossarnach.

At the time of the War of the Ring the Lord of Lossarnach was Forlong the Fat who died in the Battle of the Pelennor Fields. Morwen of Lossarnach, mother to Théoden and Théodwyn came from this region and lived there for a time with her husband King Thengel of Rohan. Ioreth, serving woman in the Houses of Healing also came from this region.