Södertälje sluss, Lock in Södertälje, Sweden.

Södertälje sluss is a lock in the Södertälje canal in central Södertälje, connecting the Baltic Sea inlet Maren with Lake Mälaren's Linasundet. Its chamber is 135 metres long and 19.6 metres wide, with a water depth over the sills of 7.80 metres. A bascule bridge called Slussbron carries traffic over the southern lock gates.

The first lock was built under engineer Eric Nordewall between 1806 and 1809, about 850 metres north of today's lock, with a 42-metre chamber and hand-operated gates. The canal was too narrow for modern ships, so it was widened in the 1920s. The current lock was inaugurated on 17 November 1924 by King Gustaf V, together with the rebuilt canal.

Locals call the lock simply Slussen, and the bascule bridge over its southern gate is Slussbron. The lock office and the pilots' house by the southern gate were built in 1924; the pilots' house was extended in 1998 but keeps its 1920s classicist form. Pilots there remotely operate all of Södertälje's bridges, from Igelstabron to Mälarbron.

The lock lies between Lotsudden and the Kusens Backe recreation area, with Slussgatan running from Marenplan to Slussbron on the west side and Grödingevägen starting on the east side. The lock is kept open to boat traffic during the Mälarprojektet rebuild, though some work stages require short interruptions. The lockkeeper's office and the pilots' house by the south gate were built in 1924.

The lock chamber measures 135 metres by 19.6 metres, with a water depth over the sills of 7.8 metres. It is the largest lock in the Nordic countries for commercial shipping. The lock's control room staff also remotely operate every bridge in Södertälje, from Igelstabron in the south to Mälarbron in the north.