The appeal result was announced as UEFA general secretary Gianni Infantino and Asian football leader Sheikh Salman bin Ebrahim al Khalifa stepped up their rivalry in the campaign to take over as head of football's scandal-tainted world body in a vote on Friday.
The bans against Blatter, FIFA president for 17 years, and UEFA president Platini were reduced from eight years to six by the appeal committee.
Both were found guilty of conflicts of interest when Blatter approved a $2 million payment to Platini in 2011 for consultancy work done without a contract a decade earlier.
He and Blatter said they would take their cases to the Court of Arbitration for Sport (CAS) in an attempt to have their bans overturned.
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The FIFA appeal body said that the ethics tribunal did not take into account "some strong mitigating factors" when determining the eight-year sanction.
Blatter and Platini again overshadowed FIFA's new attempt to turn the page on its scandal-plagued recent past with Friday's election.
Police raided a FIFA congress last May just before Blatter was elected to a fifth term. He announced he would stand down four days later.
In the absence of Platini, Infantino and Sheikh Salman, president of the Asian Football Confederation (AFC), have led a five-man race to become the new president.
The battle has been seen as too close to call in the final stages. But the election took a new twist when Prince Ali bin al Hussein went to the CAS on Monday seeking an order to force FIFA to use transparent voting booths.
The prince's lawyers had said they could seek a vote delay.
And Prince Ali, who had paid for transparent voting booths to be sent to Zurich, backed off from a move to delay the election.
"The only positive aspect of today's ruling is that the election will now go forward as planned, and the media will be closely watching for any evidence that anyone is photographing their ballot," the prince said in a statement.