St Decuman's is a Grade I listed building in Rhoscrowther, Pembrokeshire, Wales.

The parish church is on a very early Christian site and is dedicated to Saint Decuman.

It was the "bishop-house" of the cantref of Penfro and one of the seven principal churches in Dyfed under medieval Welsh law.

[2] Samuel Lewis in 1833 considered the church "not distinguished by any remarkable architectural details".

The church contains a number of tombs and memorials, including two recesses and wall-mounted coffin lids.