The Cardassian sector was a sector of space located adjacent to Sector 21503, near the Federation-Cardassian border.

In 2367 the USS Enterprise-D was conducting a mapping survey of the sector. This sector was previously visited by Captain Jean-Luc Picard while he was in command of the USS Stargazer. While there on the Stargazer he encountered some Cardassians and lowered his shields as a sign of good will, but the Cardassians took offense and attacked, taking out his weapons and damaging the impulse engines before he could retreat. (TNG: "The Wounded")