Sîn-māgir (Akkadian: 𒀭𒂗𒍪𒈠𒄫, Dsuen-ma-gir), inscribed dEN.ZU-ma-gir, “Sîn upholds,”[1] c. 1827–1817 BC (MC) was the 14th king of Isin and he reigned for 11 years.

There are currently six extant royal inscriptions, including brick palace inscriptions,[i 2] seals for his devoted servants, such as Iddin-damu, his “chief builder,” and Imgur-Sîn, his administrator, and a cone[i 3] which records the construction of a storehouse for the goddess Aktuppītum of Kiritab in his honor commissioned by Nupṭuptum, the lukur priestess or concubine, “his beloved traveling escort, mother of his first-born.”[2] An inscription[i 4] marks the construction of a defensive wall, called Dūr-Sîn-māgir, “Sîn-māgir makes the foundation of his land firm,” at Dunnum, a city northeast of Nippur.

One of the cones bearing this inscription was found in the ruins of the temple of Ninurta, the é-ḫur-sag-tí-la, in Babylon, and is thought likely to have been an ancient museum piece.

Two legal tablets offered for private sale, recording sales of a storehouse and palm grove, give a year-name elsewhere unattested, “year Sîn-māgir the king dug the Ninkarrak canal.”[i 5] Another year-name marks "(Sîn-māgir) built on the bank of the Iturungal canal (the old wadi) a great fortification (called) Sîn-māgir-madana-dagal-dagal (Sîn-māgir broadens his country)."

A province in the south and a town in eastern Babylonia near Tuplias are both called Bīt-Sîn-māgir and some historians have speculated one or other were named in his honor.