Castasegna is a former municipality in the district of Maloja in the Swiss canton of Grisons , on the Italian border. It is currently part of the municipality of Bregaglia . The town is situated in the Bergell valley, above the river Mera.

Castasegna is first mentioned in 1374 as Castexegnia.

Castasegna has an area, as of 2006, of 6.8 km2 (2.6 sq mi). Of this area, 19.2% is used for agricultural purposes, while 40.1% is forested.