Dyfed-Powys Police was called to Cwrt Henri, Dryslwyn, at about 13:50 GMT on Saturday.
The force said the fire was not being treated as suspicious but the incident is being jointly investigated with Mid and West Wales Fire and Rescue Service.
No further details were given about the cause or the age of the male victim but his next of kin have been informed.
A person has died following a house fire in Carmarthenshire.