Serra d'El-Rei ('Mountains of the King') is a Portuguese parish in the municipality of Peniche on the Atlantic Coast.

[2] Serra d'El-Rei became a town on July 1, 2003.

It was at Serra d'El-Rei that King Peter I of Portugal lived with his lover Inês de Castro.

His 14th-century castle in the town is now divided into three private living houses today.

Serra d'El-Rei is 7 km (4.3 mi) west of the historic walled-town of Óbidos, and 10 km east from Peniche.