Sector 21503
Sector 21503 was a region of space in the Alpha Quadrant. This sector was adjacent to the Cardassian sector and located near Sector 21505. The Federation-Cardassian border was located in this sector. 

During the Federation-Cardassian War, while in this sector, the  was sent to make preliminary overtures to a truce. When within range of a Cardassian warship, Captain Picard ordered the shields lowered as a measure of good faith. The warship open fired onto the Stargazer, taking out most of the weapons and damaging the impulse engines of the Federation starship. The Stargazer retreated from the sector with the warship in pursuit.

In 2367, while on a mapping survey mission, the  was attacked by a Cardassian  ship in this sector because of earlier attacks by the . ()

de:Sektor 21503
es:Sector 21503
fr:Secteur 21503
nl:Sector 21503
021503