The Afon Ysgir is a river which rises on the southern slopes of Mynydd Epynt in Powys, Wales. The tributaries known as and flow past the hamlets of Pont Rhyd-y-berry and Merthyr Cynog to combine at Pont-faen and continue past the village of Battle to join the River Usk at Aberyscir. Its upper reaches are within the military training area of , the British Army's Sennybridge Training Area.