Maredudd ap Gruffydd (1131–1155) was a prince of the kingdom of Deheubarth in Southwest Wales.
At the age of 16 he is recorded helping his half-brother Cadell, now King of Deheubarth, to expel the Normans from Ceredigion.
He then successfully defended Carmarthen castle against a Norman assault, hurling down the scaling ladders.
He survived, but was so badly injured that the effective rule of Deheubarth fell on Maredudd.
In 1153 Cadell left on a pilgrimage to Rome, leaving Maredudd as King of Deheubarth.