The Met Office warned of ice forming overnight which may lead to difficult driving conditions on untreated roads and slippery conditions on pavements.
The warning is in place from 01:00 until 10:00 GMT.
While there will be some hill snow, ice is expected to form on pavements that are wet from rain.
The warning covers Blaenau Gwent, Bridgend, Caerphilly, Carmarthenshire, Ceredigion, Gwynedd, Merthyr Tydfil, Monmouthshire, Neath Port Talbot, Newport, Pembrokeshire, Powys and Rhondda Cynon Taff.
A yellow warning of ice has been issued for 13 local authority areas in Wales on Saturday.