Ysgol Gyfun Gymraeg Plasmawr is a Welsh-medium comprehensive secondary school in Cardiff.

It opened in September 1998 as the second school of its kind in Cardiff.

Its buildings had formerly belonged to Waterhall Secondary Modern School and more recently formed Ysgol Gyfun Gymraeg Glantaf's Lower School.

The current headteacher is Dr Rhodri Thomas.

The school serves a wide area of western Cardiff that includes Culverhouse Cross, Ely, Caerau, Grangetown, Butetown, Riverside (including Pontcanna), Canton, Fairwater (including Pentrebane), Llandaff, Radyr, Creigiau, Pentyrch, and Gwaelod-y-Garth.