Mynydd Llandygái (also spelt Mynydd Llandegai, [ˌmənɨðˌɬandəˈɡai] ^ⓘ; from Welsh mynydd "mountain", Llandygai "Church of St Tegai") is a small, partly forested hill in Gwynedd, North Wales. It forms the start of the Glyderau ridge.

Mynydd Llandygái
The village of Mynydd Llandygái from Moelyci, showing the two rows of houses, and the slate quarries beyond
Mynydd Llandygái Location within Gwynedd
OS grid reference	SH603655
Community	Llandygai
Principal area	Gwynedd
Country	Wales
Sovereign state	United Kingdom
Post town	BANGOR
Postcode district	LL57
Dialling code	01248
Police	North Wales
Fire	North Wales
Ambulance	Welsh
UK Parliament	Arfon
Senedd Cymru – Welsh Parliament	Arfon
List of places UK Wales Gwynedd 53°10′05″N 4°05′20″W / 53.168°N 4.089°W / 53.168; -4.089

It is also the name of the quarry village at the base of the hill situated at the edge of Snowdonia National Park at grid reference SH600656. The village lies at about 1,000 feet (300 m) above sea level and gets strong winds and above average rainfall. Many of the houses are spread along long roads rather than clustered around a point, giving the village a somewhat decentralised feel. However the village is distinguished by two parallel rows of semi-detached quarrymen's cottages constructed during the 19th century for workers of Penrhyn Quarry, which mined slate. The first mention of housing on the site can be found in the census of 1841. Each of the houses was provided with an area of land (approximately 1 acre) sufficient to feed the family. This arrangement is clearly visible on the map of the area. This can be contrasted with the situation in the South Wales coalfields or in the industrial Midlands where no such provision was made for the workers.

Originally named Douglas Hill, the name was changed in the 1930s after the inhabitants decided that they did not want to associate with the name Douglas, namely part of the Penrhyn family surname. (See Baron Penrhyn.)

Physically the village has changed little since it was originally built.

The area to the south is mountainous and there are a number of slate and stone quarries in the vicinity.