Maredudd ap Gruffydd (1130–1155) was a prince of the kingdom of Deheubarth in south west Wales.
Maredudd was the eldest son of Gruffydd ap Rhys by Gwenllian ferch Gruffydd, though he had two older half-brothers, Anarawd and Cadell. He was only six years old when his mother and then his father were killed. At the age of 16 he is recorded helping his half-brother Cadell, now prince of Deheubarth, to expel the Normans from Ceredigion. He then successfully defended Carmarthen castle against a Norman assault, hurling down the scaling ladders.
In 1151 he took a prominent part in winning back the northern part of Ceredigion from Gwynedd. The same year Cadell was attacked by a force of Normans while out hunting and left for dead. 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 prince of Deheubarth.
Maredudd died two years later in 1155, leaving the throne of Deheubarth to his younger brother Rhys, later known as The Lord Rhys.