Banjarbaru is the capital city of South Kalimantan, one of the provinces in Indonesia. It is located 35 km (22 mi) southeast of Banjarmasin, the largest city of the province. The city had a population of 199,627 as of the 2010 Census, and 253,442 at the 2020 Census, and the official population estimate (as at mid 2024) was 285,546 (comprising 143,255 males and 142,291 females). The large town of Martapura, with 158,186 inhabitants in 2024 (in Martapura and Martapura Timur Districts), lies immediately to the north of Banjarbaru in Banjar Regency, and in effect constitutes an extension of the city. The second largest city in the province after Banjarmasin, it is also part of Banjarbakula metropolitan area.

Banjarbaru was previously only a temporary name used by governor Dr. Murdjani to differentiate it from Banjarmasin, as "baru" means "new" in Indonesian. However, the name stuck between people living there and gradually became official name of the city. Banjarbaru previously consisted of a series of hills known as Mount Apam.

Diamond mines in Cempaka have existed since the 15th century under the Hindu-Buddhist kingdom Negara Dipa. In the era of the Banjar Sultanate, there was a royal edict stating that diamonds of four carats or higher should be sold only to the sultan. The place was mostly uninhabited except for resting places of diamond mine laborers from Cempaka, now also part of the city. Cempaka diamond mines under the colonial era were regulated under Ordonantie 25 Nopember 1923 Staatblast 1923 No. 174 together with Pelaihari and Martapura.

In the 1950s, because of frequent floods that disrupted government activities in Banjarmasin, it was suggested to relocate the capital of then-Kalimantan province to a new city. The construction and city planning was assisted by a Dutch-descendant architect named D.A.W. Van der Pijl based on the European city concept, which explains the abundance of city parks and a city hall in the center of the city. However, the plan to relocate the provincial government was never realized fully. As of April 2021,^[update] only the South Kalimantan governor's office has been relocated, while the parliament is still in Banjarmasin.

The city was previously intended by Sukarno to be new center of the steel industry in Kalimantan with assistance from the Soviet Union to develop it. Cooperation between the two was formalized on 11 September 1956. However, the plan to construct steel factories was never realized until after the 30 September Movement and subsequent purge of communism in Indonesia. Traces of Soviet projects can be seen in the city such as with Mess L.

On 20 April 1999, Banjarbaru was separated from Banjar Regency (of which it had previously been a part) and gained its status as an independent city, although it was still recognized as part of the Banjarbakula metropolitan area. The city legally became capital of the South Kalimantan province on 15 February 2022 following updates of laws concerning legal basis of several provinces were passed by People's Representative Council.

Banjarbaru is located at the foot of the Meratus Mountains, with 80% of the city area elevated between 0 and 25 m (82 ft) above sea level, but it also includes areas up to 500 m (1,600 ft) high. In the North, East, and West it borders Banjar Regency, while in the South it borders Tanah Laut Regency. Podzol dominates the city soil, with a concentration of as much as 63.82%. However, Landasan Ulin's soil is instead dominated by peat and alluvium.

Compared to other regencies and cities in the province, Banjarbaru is also the second smallest second-level administrative division in the province after Banjarmasin city, covering around 0.88% of province territory.