The Mempa sector is a region of space within the Klingon Empire, where the Mempa system and Beta Thoridar are located.
Several forces allied with Captain Kurn were stationed in the Mempa sector before the outbreak of the Klingon Civil War. When Worf convinced Kurn to support Gowron, Kurn had to go to the Mempa sector to meet with the other squadron commanders in order to convince them to support Gowron as well. (TNG: "Redemption")
Following the outbreak of war, Gowron's forces were able to destroy the Duras' forces supply lines in the Mempa sector. Three weeks later, the forces loyal to the Duras family had rebuilt their lines in the sector, thanks to Romulan support, and defeated Gowron's forces in the Mempa system, forcing them to retreat to Beta Lankal. (TNG: "Redemption II")