Saint-Ghislain (; ; ) is a city and municipality of Wallonia located in the province of Hainaut, Belgium.
On 1 January 2018 the municipality had 23,335 inhabitants. The total area is , giving a population density of .
The municipality consists of the following districts: Baudour, Hautrage, Neufmaison, Saint-Ghislain, Sirault, Tertre et Villerot.
The town is named after Saint Ghislain. 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. Ursidongus was later named after him.
Google chose Saint-Ghislain in 2007 to host its new major European datacenter.