The siege of Zbarazh (Ukrainian: Облога Збаража, Битва під Збаражем, Polish: Oblężenie Zbaraża, Bitwa pod Zbarażem; 10 July – 22 August, 1649) was a part of the Khmelnytsky Uprising, and occurred in and around the site of the present-day city of Zbarazh in Ukraine. The Cossack Hetmanate and Crimean Khanate combined forces against the Polish–Lithuanian Commonwealth in a siege that lasted seven weeks.

The Polish–Lithuanian forces remained under siege in Zbarazh Castle until after the conclusion of the nearby Battle of Zboriv on 15–16 August 1649 and the Treaty of Zboriv two days later.

In the first half of 1649, the Polish–Lithuanian Commonwealth negotiations with the rebellious Cossacks fell through, and the Polish–Lithuanian military began gathering near its borders with the insurgent-held Ukraine. While the king organized the main Polish army, and Janusz Radziwiłł commanded the Lithuanian army along the Horyn River, an army under three regimentarzs (Andrzej Firlej, Stanisław Lanckoroński and Mikołaj Ostroróg) was located in Zbarazh from 30 June, where Prince Jeremi Wiśniowiecki arrived with reinforcements on 7 July. Wiśniowiecki's arrival raised the morale of the royal army, and despite his lack of a military rank, both the common soldiers and the new regimentarz promised to heed his advice, and he was offered the official command (which he refused).

Detachments from the Castellan of Kamianiec Stanisław Lanckoroński, Starosta of Lwow Adam Hieronim Sieniawski, Starosta of Braclaw Jerzy Kalinowski, and Prince Samuel Karol Korecki, also arrived in the area.

Zbarazh Castle was rebuilt in the decades preceding the siege under the Netherland engineer Henryk van Peene, who finished his project in 1626. The castle's outer walls formed a square about 88 meters on each side, surrounded by an earthen wall and a moat. It was a relatively modern and resilient construction, whose major weakness was its small size, with little space for an extensive army and supplies. Built with earlier Tatar raids in mind, it was not meant to withstand a prolonged siege by a large army. The town itself had relatively poor defenses. The Polish–Lithuanian fortified camp incorporated the town defenses and the castle.

The Polish–Lithuanian forces numbered between 10,000 and 15,000, according to different sources, and Widecki notes that the lower number accounts for regular troops, whereas the higher one probably counts auxiliary troops such as armed servants and the town militia.

The Polish–Lithuanian forces were commanded officially by Andrzej Firlej. However, as noted by Polish historian Widacki, Firlej had little authority, and often took the advice of Wiśniowiecki, who might be seen as the real commander of the Polish–Lithuanian forces. As a contemporary memoir notes, Wiśniowiecki's opposition was enough to veto a plan proposed and backed by all three regimentarzs. Each of the regimentarz, as well as Wiśniowiecki, commanded a division of the troops, tasked with defending a part of the line; there were five divisions in total, with the last one commanded by chorąży Aleksander Koniecpolski.

The forces of the allied Zaporozhian Cossacks and Crimean Tatars at Zbarazh numbered around 130,000, with two thirds of those being Cossacks. Widecki notes that the number of 70,000 Cossacks given by some sources may be true in so far as it reflects the size of the seasoned, regular Cossack troops, with the difference reflecting the size of the Cossack militia and rebellious peasants. Those forces were commanded by the Cossack leader Bohdan Khmelnytsky and the Tatar khan İslâm III Giray.