Ukrainian President Petro Poroshenko has dismissed Igor Kolomoyskyi, governor of the eastern Dnipropetrovsk region, the president's official web site said on Wednesday.
"Igor Valeryevich Kolomoyskyi is dismissed from the post of the chairman of Dnipropetrovsk regional administration," the decree published on the web site said.
Valentin Reznichenko has been appointed as acting Dnipropetrovsk governor.
Kolomoyskyi - who is estimated to be worth more than $2 billion - has been widely credited with helping bring order in Dnipropetrovsk and halt the advance of pro-Russian rebels further to the east, BBC reported.
He is also financing a number of Ukrainian battalions fighting the separatists in the Donetsk and Luhansk region.
His resignation comes days after armed men suspected of acting on orders from the oligarch briefly seized the headquarters of the Ukrnafta energy company and its subsidiary UkrTransNafta.
