To obtain a highly spin polarized positron beam, Ge-68 isotope have been produced using a nuclear reaction of Ga-69(p,2n)Ge-68. As target materials, we examined a metal form Ga-69 stable isotope and a GaN substrate. By 20 MeV proton irradiation, the production of Ge-68 source was confirmed in both targets. The production rates of Ge-68 were 0.16 and 0.53 MBq/mu A/h for the metal Ga and GaN target, respectively. The spin polarizations of positrons emitted from Ge-68 was estimated to be approximately 50 to 70%.