Grez-Doiceau is a Belgian municipality located in the province of Walloon Brabant. On January 1, 2006, Grez-Doiceau had a total population of 12,403. The total area is 55.44 km² which gives a population density of 224 inhabitants per km². Grez-Doiceau is watered by the Train, a tributary of the Dyle.
The municipality consists of the following sub-municipalities: Archennes (Eerken), Biez, Bossut-Gottechain, Grez-Doiceau proper, and Nethen.