The Serie A leaders have secured the services of young Dutch midfielder, whose contract with the Amsterdam club expired at the end of the current campaign.
The Eredivisie Champions cashed in on the starlet as his contract expired in the summer, despite Ajax technical director Danny Blind expressing his desire to keep Bouy, having proposed him a four-year deal in December.
"Ouasim is a big talent and we would have loved to keep him here," Blind told the club's official website.
"We opened talks about a new contract in December and offered him a four-year deal. We did not reach an agreement, though.
"Juventus made him a great offer that he could not turn down. By selling him now, we have at least received a transfer fee.
"We wish him all the best, but are disappointed that we were unable to hold on to him."
Bouy, who broke into Ajax's senior team earlier in 2012, did not make a single Eredivisie appearance for the Dutch club, but is widely considered as one of of Europe's most exciting talents.
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