Saint-Ghislain (French pronunciation: [sɛ̃ ɡilɛ̃] ⓘ; Picard: Saint-Guilagne; Walloon: Sint-Guilin) is a city and municipality of Wallonia located in the province of Hainaut, Belgium.

The total area is 70.18 square kilometres (27.10 sq mi), giving a population density of 333 inhabitants per square kilometre (860/sq mi).

The municipality consists of the following districts: Baudour, Hautrage, Neufmaison, Saint-Ghislain, Sirault, Tertre et Villerot.

In the 7th century, with two unknown disciples Ghislain made a clearing in the vicinity of Castrilocus (now Mons), later taking up his abode at a place called Ursidongus, where he built an oratory or chapel dedicated to Saints Peter and Paul.

Google chose Saint-Ghislain in 2007 to host its new major European datacenter.