Mortsel is a city and municipality close to the city of Antwerp located in the Belgian province of Antwerp. The municipality only comprises the city of Mortsel proper. On January 1, 2006 Mortsel had a total population of 24,427 people. The total area is 7.78 km² which gives a population density of 3,138 inhabitants per km². This is the highest population density of any municipality in the Flemish Region (Flanders), and second-highest (to Saint-Nicolas) outside the Brussels-Capital Region.

The city consists of the areas Mortsel-Dorp, Oude-God and Luithagen. Mortsel is bordered by Antwerp (districts Wilrijk, Berchem and Deurne), Borsbeek, Boechout, Hove, and Edegem.

The headquarters of Agfa-Gevaert are situated in Mortsel.

Mortsel was the victim of one of the major tragedies and errors of World War II. On April 5, 1943, the bombing of the Minerva car factory, then used to repair Luftwaffe planes, was the target of a big bombing raid by the Allies, but the target was missed and a residential area hit instead, resulting in the death of 936 civilians, including 209 children. The last V2 launched against Antwerp also fell in Mortsel, killing 27 people, on March 27, 1945.