Llanfyrnach Rural District was an administrative division of Pembrokeshire, Wales. It was created in 1894 from the part of Newcastle in Emlyn Poor Law Union situated in Pembrokeshire, and consisted of six civil parishes: Capel Colman, Castellan, Clydau, Llanfyrnach, Penrydd and West Cilrhedyn. It continued to be administered from Newcastle Emlyn. It was abolished in 1934, when it was amalgamated with St Dogmells RD to form Cemaes RD.