The court did, however, cut Svetlana Bakhmina's sentence from seven to six-and-a-half years.
Bakmina was jailed in April for tax evasion and embezzlement.
The founder of Yukos, Mikhail Khodorkovsky, is imprisoned on similar charges.
Yukos itself has been declared bankrupt for its failure to pay a massive bill for unpaid taxes.
(compiled from agency reports)