The FIFA Disciplinary Committee’s sanctions mean the defending La Liga champions cannot buy or sell players until the transfer window opens in the summer of next year.
Barcelona was found to have “violated several provisions concerning the international transfer and first registration of non-Spanish minors with the club, as well as other relevant regulations with regard to the registration and participation of certain players in national competitions”.
The club broke the rules in its signing of 10 players.
It has been fined CHF 450,000 (£305,000/$508,000/€369,000) and given 90 days to “regularise the situation of all minor players concerned”.
The Spanish Football Federation (RFEF) has also been sanctioned for the same “serious” breaches, being handed a fine of CHF 500,000 (£339,000/$565,000/€410,000).
It has been given a year to “regularise their regulatory framework and existing system concerning the international transfer of minors in football”.
The sanctions follow investigations initially conducted by FIFA Transfer Matching System GmbH (FIFATMS) last year.
A FIFA spokesman said: “The Disciplinary Committee underlined that FIFA takes the protection of minors in football very seriously.
“The protection of minors is one of the key principles included in the agreement concluded between FIFA, UEFA and the European Commission in 2001.
“The Disciplinary Committee acknowledged that young football players are vulnerable to exploitation and abuse in a foreign country without the proper controls.
“This particular fact makes the protection of minors in football by the sport’s governing bodies, especially by FIFA, even more important.”
FIFA added international transfers of minor players are allowed under three “limited circumstances”,
Barcelona has been involved in recent controversy over signings, after it revealed it paid more for Brazilian star Neymar than had originally been stated when the 22-year-old joined the club last year.
It emerged that as part of the total £71.5 million ($118 million/€86 million) paid for Neymar, there was a £33 million ($54 million/€39 million) compensation fee paid to his father to ensure he joined Barcelona.
Club president Sandro Rosell resigned after being accused of misappropriating funds in the deal, and a criminal investigation is ongoing over claims of tax evasion.
The club currently lie second in La Liga, one point behind Atlético Madrid, who they drew with at the Camp Nou in their Champions League quarter-final first leg encounter last night.