威尔士第四台（威尔斯语：Sianel Pedwar Cymru，简称：S4C）是威尔斯一家电视台，1982年11月1日开播。S4C有两条信号：模拟信号以双语（威尔斯语及英语）广播；数码信号则只以威尔斯语广播。其中英语节目主要由英国第四台提供。2010年模拟信号停播，该频道完全使用威尔士语广播。

S4C (Welsh pronunciation: [ɛs ˈpʰɛdwar ɛkʰ], from the Welsh Sianel Pedwar Cymru, meaning "Channel Four Wales") is a Welsh-language public-service television channel based in Cardiff and broadcast throughout Wales.

The first television channel to be aimed specifically at a Welsh-speaking audience, S4C is (after BBC One, ITV, BBC Two and Sky1) the fifth-oldest television channel in the United Kingdom (Channel 4 was launched in the rest of the country one day later.) Its chief executive since April 2012 is Ian Jones.