The Marcan system was a star system within the Klingon Empire, in or near the Allicar sector, consisting of at least five planets.

The Marcan system was one of the first conquered by the Klingons during their early days of expansion. It was a resource-rich system, which made it strategic target of the Empire's enemies. (GKN short story: "A Song Well Sung")

The Marcan system was the site of a key battle during the closing days of the Dominion War. Twelve Klingon vessels managed to defend the system from six Jem'Hadar and Breen ships, allowing a subsequent offensive into the Allicar sector. (TNG novel: Diplomatic Implausibility)

See also: Marcan V