As a result, Barca, who were found guilty of breaching rules on the international transfer of under-18s, will be banned from registering players during January as well as the 2015 summer window, FIFA said.
FIFA also rejected Barcelona's appeal against a £300,000 fine and have been given 90 days to regularise the situation off all the minor players concerned, the governing body said. The ban was originally imposed in April and would have covered the current transfer window, followed by the next one in January.
However, Barcelona appealed later the same month and the ban was lifted pending the outcome of the disciplinary process.
Barca have since signed the Uruguay forward Luis Suarez, himself serving a four-month ban from football, for £65m pounds, the Belgium centre-back Thomas Vermaelen, the France defender Jeremy Mathieu, the Croatia midfielder Ivan Rakitic and two goalkeepers.
"The FIFA Appeal Committee has decided to . . . confirm in their entirety the decisions rendered by the FIFA Disciplinary Committee in the respective cases relating to the protection of minors," said FIFA.