The 2021 4 Hours of Monza was an endurance sportscar racing event held on 11 July, 2021, at Monza Circuit. It was the fourth round of the 2021 European Le Mans Series.
The entry list was revealed on 30 June 2021, and saw 44 entries: 19 in LMP2, 16 in LMP3 and 9 in LMGTE. The No. 32 United Autosports Oreca 07-Gibson entry was withdrawn after Job van Uitert contracted COVID-19.
Class winners are marked in bold and .