Kaijō (海上郡; -gun) was a district located in Chiba, Japan.
As of 2003, the district had an estimated population of 21,982 and a density of 469.10 persons per km². The total area was 46.86 km².
Until the day before the district dissolved (June 30, 2005), the district had two towns.
On July 1, 2005, these two towns merged with the town of Hikata from Katori District and the city of Asahi to form the city of Asahi, which will simply dissolve Kaijo District.