Kvarnsjön is a long narrow lake at Lissma in Huddinge Municipality, Södermanland.

The surrounding land is part of Tyresån's main catchment area.

Kvarnsjön is surrounded mainly by lean pine woodland and marshland.

After the mill, low walls of chipped gray stone blocks remain on either side of the stream.

The mill has lent its name to Lissma Kvarntorp, a residential area consisting of holiday homes and permanent housing.