Grändalssjön (Swedish for "Lake of Grändalen") is a small lake in Tyresö Municipality south-east of central Stockholm, Sweden.

Immediately north of Grändalssjön is the Raksta open-air area, and Övre kärret ("Upper Swamp"), a swampy lake, is located west of the lake.

Two small cottages located nearby, Grändalen and Skansen, are part of Gamla Tyresö.

[3] It is virtually unaffected by eutrophication and human activities.

[4] Aquatic vegetation is dominated by Fragile Stonewort.