Untxillaitz, Untxillaitx, or Untzillatx, is a mountain of Biscay, Basque Country (Spain), 934 m. high. Its name may mean "Rabbit's peak" untzi(a)=rabbit aitz=peak.Part of the Urkiola range, although it does not belong to the same crest of the Anboto, it is also part of the same limestone range.It forms the pass of Atxarte with the neighnouring Aitz Txiki and it's located in the valleys of Mendiola and Mañaria.