The Collaborative International Dictionary of English v.0.48:

Denationalize \De*na"tion*al*ize\, v. t. [imp. & p. p.
   Denationalized; p. pr. & vb. n. Denationalizing.] [Cf. F.
   d['e]nationaliser.]
   1. To divest or deprive of national character or rights.
      [1913 Webster]

            Bonaparte's decree denationalizes, as he calls it,
            all ships that have touched at a British port.
                                                  --Cobbett.
      [1913 Webster]

            An expatriated, denationalized race.  --G. Eliot.
      [1913 Webster]

   2. to change (something, as an industry or business) from
      state to private ownership or control; as, the British
      denationalization of steel.

   Syn: privatize, denationalise.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

denationalize
    v 1: put under private control or ownership; "The steel industry
         was denationalized" [syn: denationalize, denationalise]
         [ant: nationalise, nationalize]