It has municipal jurisdiction over 117,000 dunams, 6,000 of which is built-up area and 11,715 of which is cultivated. The main economic activities in Sa'ir are agriculture and the Israeli labor market, although the latter has been adversely affected as a result of the Israeli restrictions following the Second Intifada in 2000–04. Olives are the major cash crop.
According to the Applied Research Institute Jerusalem (ARIJ), Sa'ir "was established on the town of Saeer (صعير) or Saiour (صعيور)", and during the Roman era the town was known as "Sior". The Book of Joshua (15:54) mentions a town in this area called Tsi`or (ציער, also transliterated Sior or Zior). The Hebrew name is related to a root meaning "small".
Byzantine ceramics have been found. The PEF's Survey of Western Palestine (SWP), wrote that: "The tomb of El 'Ais (Esau), south of the village, is in a chamber 37 feet east and west by 20 feet north and south, with a Mihrab on the south wall. The tomb is 12 feet long, 3 1/2 feet broad, 5 feet high, covered with a dark green cloth and a canopy above. An ostrich egg is hung near. North of the chamber is a vaulted room of equal size, and to the east is an open court with a fig-tree, and a second cenotaph rudely plastered, said to be that of Esau's slave. Rock-cut tombs exist south-west of this place."
In 1596 Sa'ir appeared in the Ottoman tax registers as part of the nahiya of Halil in the Liwa of Quds. It had an entirely Muslim population consisting of 72 households. Taxes were paid on wheat, barley, summer crops, olive trees, goats and/or beehives.
The French explorer Victor Guérin visited the village in the 1860s, and found it having about 400 inhabitants.SWP described Sa'ir in 1883 as "a village of moderate size, in a valley surrounded with cultivated ground." A maqam (shrine) located in Sa'ir was believed by the local Muslims to house the tomb of Esau who they referred to as "Aisa." The SWP stated this identification was false and that Esau's tomb was in the Biblical Mount Seir.
Under the name Sa'in, an Ottoman village list of about 1870 indicated 84 houses and a population of 186, though it is proposed that the population count included men, only.
In the 1945 statistics the population of Si'ir was 2,710, all Muslims, who owned 92,423 dunams of land according to an official land and population survey. 2,483 dunams were plantations and irrigable land, 10,671 for cereals, while 76 dunams were built-up (urban) land.
Following the 1993 Oslo Accords Sa'ir was designated within "Area B" giving the Palestinian National Authority (PNA) control over the town's civil affairs while Israel maintained its control over security. In 1997, an elected 13-member municipal council was established by the PNA to administer Sa'ir. Its municipal borders include a number of small villages, including al-Uddeisa, ad-Duwwara, Irqan Turad, Kuziba, Wadi ar-Rum and Ras at-Tawil. Principal families include Shlaldah, Froukh, Al-Lahaleeh, Jaradat, Mtur, al-Jabarin, al-Kawazbeh, Arameen and al-Turweh. Hakim Shlaldah was elected mayor in the 2005 municipal elections.
In January, 2013, Rafat Jaradat, 30 years old, from Sa'ir, died in jail five days after he was arrested by the Israelis. Israeli sources said his death was caused by "sudden heart attack while under interrogation", while Palestinian officials said that Jaradat had been tortured while in Israeli detention. His body had bruises and broken ribs, which the Israelis said came from attempts to revive him, while his brother said it looked as if Jaradat had been severely beaten.
Hamas candidates have won election to the town council, which is described in the Israeli press as "Hamas affiliated," and as "having close ties to Hamas."
Between October 2015 and mid January 2016 eleven Sair residents were shot dead by the Israeli army in alleged attacks on Israeli soldiers. Almost half of them were killed at Beit Einun Junction where the IDF controls access to the town.
^U. O. Schmelz (1990). "Population characteristics of Jerusalem and Hebron regions according to Ottoman census of 1905". In Gad G. Gilbar (ed.). Ottoman Palestine 1800–1914. Leiden: E. J. Brill. pp. 15–67.
^Barron, 1923, Table V, Sub-district of Hebron, p. 10