The Diocese of Zrenjanin is a Latin Church ecclesiastical territory or diocese of the Roman Catholic Church in Serbia. It is subject to the Roman Catholic Archdiocese of Belgrade. The Diocese is centered in the city of Zrenjanin.

Zrenjanin is a city and the administrative center of the Central Banat District in the autonomous province of Vojvodina, Serbia. The city urban area has a population of 67,129 inhabitants, while the city administrative area has 105,722 inhabitants. The old name for Zrenjanin is Veliki Bečkerek or Nagybecskerek as it was known under Austria-Hungary up until 1918. A thousand Catalans founded on 1735 New Barcelona in a place which is now the suburb of Dolja within Zrenjanin, exiled from the War of the Spanish Succession. After World War I and the liberation of Veliki Bečkerek the new name of the city was Petrovgrad, in honor of His Majesty King Peter I the Great Liberator, the King of Serbia and the King of Serbs, Croats and Slovenes.