The 27-year-old has moved on a free transfer after finding himself surplus to requirements at Boro and has rejoined the Amsterdam club with whom he had a two-year spell earlier in his career.
Ajax boss Martin Jol told the club's official website: "We needed an extra striker and we have limited resources which have to be considered."
Mido has had a nomadic existence after leaving Ajax in 2003, playing for Celta Vigo, Marseille, Roma, Tottenham, Wigan, Zamalek and West Ham.
Source: PA
