South Sudanese President Salva Kiir on Monday sacked Finance Minister Stephen Dhieu Dau and replaced him with Salvatore Garang Mabiordit.
Kiir also removed Marial Chanoung from his position as chief of operations, training and intelligence in the national army, the Sudan People's Liberation Army.
A presidential decree announced on the state-owned radio Monday evening did not give any reason for the firing of the officials.
Dau became South Sudan's finance minister in July 2016 when he immediately embarked on radical financial reform policies seeking to tackle a biting economic crunch.
Dau's successor previously served in the Finance Ministry as undersecretary until January 2017, when he was transferred to the Ministry of Trade and Industry as technical adviser.
The oil-rich east African nation depends on oil revenue for 98 percent of government budget but production has declined due to conflict and falling global oil prices.
Chanoung was among six senior South Sudanese government and opposition military officials sanctioned by the United Nations in July 2015 for allegedly undermining peace efforts and hampering delivery of humanitarian aid.