A city east of the Jordan, in or near Gilead (Numbers 32:1,3; c.), and inhabited by the Amorites. It was taken by a special expedition sent by Moses to conquer it (Numbers 21:32). From the Septuagint, which reads Ἰαζήρ for 
in Numbers 21:24, it appears that Jaazer was on the border of Ammon. As an important city it gave its name to the whole of the surrounding territory (ib. 32:1). Even a "sea of Jaazer" is mentioned in Jeremiah 48:32 (but comp. the Septuagint rendering πολις Ιαζήρ, probably due to reading 
instead of 
).
Jaazer is stated to have been a fertile land fit for the raising of cattle (ib.) and a place having many vineyards (Isaiah 16:8,9; Jer. c.). It was occupied by the children of Gad (Joshua 13:25; 1 Chronicles 26:31), by which tribe it was allotted to the Merarite Levites (Joshua 21:39; 1 Chronicles 6:66 [A. V. 81]). In the time of David it seems to have been occupied by the Hebronites, who were descendants of Kohath (1 Chronicles 26:31). It was chosen as one of the stations by David's officers who were sent to number the children of Israel (2 Samuel 24:5).
According to Josephus ("Ant." 12:8, § 1), Jaazer was captured and burned by Judas Maccabeus. The site of Jaazer was defined by Eusebius and Jerome ("Onomasticon," s. "Azor") as being 8 or 10 Roman miles west of Philadelphia, and 15 miles north of Heshbon, and as the source of a large river falling into the Jordan. It is identified by some scholars (e.g., S. Merrill; see Hastings, "Dict. Bible," s.) with the modern Khurbat Ṣar on the road from 'Iraḳ al-Amir to Al-Salt; but this identification has been rejected by Cheyne (Cheyne and Black, "Encyc. Bibl." s.).