Powys Wenwynwyn or Powys Cyfeiliog is the southern portion of the former princely state of Powys, which splits following the death of Madog ap Maredudd of Powys in 1160.

The realm is split, with the northern portion (Maelor) going to Gruffydd Maelor and becoming known, eventually, as Powys Fadog and the southern portion (Cyfeiliog) going to Owain Cyfeiliog and becoming known, eventually, as Powys Wenwynwyn after Prince Gwenwynwyn ab Owain, its second ruler.Powys Wenwynwyn and Gwynedd become bitter rivals in the years that follow with the former frequently allying itself with England to further its own aims in weakening the latter.