The River Lledr (Welsh: Afon Lledr) is a river in North Wales and a tributary of the River Conwy.
The Lledr has its source on the eastern slopes of Ysgafell Wen, which lies between Moel Siabod and Cnicht. It flows in a north-easterly direction towards Blaenau Dolwyddelan, where Ceunant Ty'n y Ddol joins it, then flows under the so-called Roman Bridge (Welsh: Pont Rufeinig) and past Dolwyddelan, where Afon Penamnen joins it. It continues to the north-east past Pont-y-Pant and then east along the Lledr Valley, running parallel to the A470 and the railway line from Blaenau Ffestiniog to Llandudno with stations in the Lledr Valley at Roman Bridge, Dolwyddelan, and Pont-y-Pant. The river joins the River Conwy to the south of Betws-y-Coed.