The Seeztal (English: Seez Valley) is a valley in the Canton of St. Gallen , Switzerland , extending to the east of Lake Walen (Walensee) for some 10 km (6.2 mi) and followed by the lower portion of the river Seez (its upper portion flows through the Weisstannental).

The Seeztal appears to be a left branch off the Alpine Rhine valley at Sargans , but there is a divide at Mels .

Situated in the Seeztal are the municipalities of Walenstadt (425 m (1,394 ft) a.s.l.), Flums (453 m (1,486 ft) a.s.l.) and Mels (500 m (1,600 ft) a.s.l.).

The Seeztal lies along the shortest route between the cities of Chur (the capital of the canton of Grisons ) and Zürich (Switzerland's largest city). Running along the valley are the A3 motorway and the Ziegelbrücke–Sargans railway line.