Kirkjubæjar Abbey (Icelandic: Kirkjubæjarklaustur), in operation from 1186 until the reformation, was a monastery in Iceland of nuns of the Order of St. Benedict. It was located at Kirkjubæjarklaustur. Iceland had nine religious communities before the Reformation, two of which were monasteries of nuns, of which this is the first and oldest.
In contrast to the other women's monastery in Iceland, Reynistaðarklaustur (1295-1563), which was placed under the authority of the Bishop of Hólar, at Kirkjubæjar Abbey the Abbess was left in full authority over the community, free of episcopal oversight.
The place names of Systrafoss (the waterfall of the Sisters) and of Lake Systravatn in the mountains above the village refer to this abbey. Folk tales illustrate history with stories about both good and sinful nuns. The Systrastapi (Sister's rock) is where two nuns of the Abbey were buried after being burned at the stake. One of the nuns was accused of selling her soul to the Devil, carrying the Blessed Sacrament outside the church, and having carnal knowledge with men. The other was charged with speaking blasphemously of the Pope. After the Reformation, the latter nun was vindicated, and flowers are said to bloom on her grave, but not that of the first nun. This is said to have occurred in 1343.
Systravatn also has a legend related to the cloister. The nuns traditionally bathed in the lake, and one day two nuns saw a hand with a gold ring extending from the water. When they tried to seize the ring, they were dragged below the water and drowned.
The abbey was regarded as a center of culture and literature. In 1402, most of the abbey's servants and many nuns died of the plague, and the nuns themselves were, for a period, forced to tend to the cattle. This they are said to have done badly, as the majority of them were from wealthy families and unused to manual labor. During the Reformation, Kirkjubæjar Abbey was dissolved, but the nuns were allowed to remain there for life. The former nuns are last mentioned in 1544, when six of them were still in residence in the abbey buildings.