The Mempa system is a Klingon star system located in the Mempa sector.
The system was the site of several key battles during the Klingon Civil War of 2367-2368. Forces loyal to Gowron suffered a major defeat against the House of Duras in the Mempa system during the conflict. Sela assured B'Etor that Gowron's forces would not be a threat in region for some time. (TNG: "Redemption II").
In 2373, when Pahash (actually, Miles O'Brien posing as a Klingon) was questioned by Martok (actually, a Changeling posing as Martok) why he looked familiar, Pahash suggested that perhaps they met on the battlefield, adding that his regiment fought at Mempa. Martok, who was not entirely convinced, recalling Mempa, stating that "many noble deeds were done on that dark day." (DS9: "Apocalypse Rising")