Flénu is a sub-municipality of the city of Mons located in the province of Hainaut, Wallonia, Belgium. The municipality of Flénu was formed on 8 June 1870, when it was detached from the municipality of Jemappes. In 1971, Flénu was merged into Jemappes. On 1 January 1977, Jemappes was merged into Mons.