The 26-year-old joins the Premier League club on a deal until the end of the season and will be reunited with Martin Jol, who managed the Amsterdam club in 2009-10
The midfielder, a Cameroon international, has made over 130 appearances for the Amsterdam giants since joining the club in 2008.
Ajax technical director Marc Overmars confirmed earlier on Thursday that there had been an enquiry for Enoh from the Cottagers.
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The signing of the central midfielder was Fulham's third of transfer deadline day, having also wrapped up loan moves for right-back Stanislav Manolev and AC Milan's versatile Dutchman Urby Emanuelson.
The London side had previously completed the loan signing of Arsenal midfielder Emmanuel Frimpong on Monday.