中古威尔斯语（Cymraeg Canol）指12世纪至14世纪之间的威尔斯语。此语言在威尔斯的中世纪民间故事集马比诺吉昂手稿中完整地保留下来，尽管故事本身可追溯至更早的年代；除此之外，中古威尔斯语也是威尔斯法手稿中所使用的语言。即使需要一点额外的学习，中古威尔斯语对于现代的威尔斯语用户来说还是种可理解的语言。

中古威尔斯语在语音方面和现代威尔斯语仅有些许不同 (Evans 1964)。字母 "u" 在现代威尔斯语北方及南方方言中分别代表 /ɨ/ 和 /i/，但在中古威尔斯语里是代表闭央圆唇元音的 /ʉ/。中古威尔斯语里在非重音的末音节中出现的双元音 "aw" 在现代威尔斯语中则变成 "o"（例：中古威尔斯语 marchawc = 现在威尔斯语 marchog「骑马者」）。类似的例子：中古威尔斯语的双元音 "ei" 和 "eu" 在末音节中也已变成 "ai" 和 "au"，例如中古威尔斯语 seith = 现代威尔斯语 saith「七」；中古威尔斯语 heul = 现在威尔斯语 haul「太阳」。

Middle Welsh (Welsh:Cymraeg Canol) is the label attached to the Welsh language of the 12th to 14th centuries, of which much more remains than for any earlier period. This form of Welsh developed from Old Welsh.

Middle Welsh is the language of nearly all surviving early manuscripts of the Mabinogion, although the tales themselves are certainly much older. It is also the language of most of the manuscripts of Welsh law. Middle Welsh is reasonably intelligible, albeit with some work, to a modern-day Welsh speaker.