President Salva Kiir has relieved the SPLA Chief of General Staff, General Paul Malong Awan.
General Malong was removed from office in a decree on Tuesday.
He has been replaced by General James Ajonga Mawut, who was the deputy chief of general staff for administration and finance.
The changes were made in separate decrees broadcast on SSBC TV on Tuesday night.
Before his appointment as the Chief of General Staff in April 2014, General Malong was the governor of the former Northern Bhar al-Ghazal State.
He took over as Chief of General Staff of the SPLA from General James Hoth Mai less than a year after the conflict began in December 2013.