Some full-Heusler alloys, such as Co(2)MnSi and Co(2)MnGe, are expected to be half-metallic ferromagnetic material, which has complete spin polarization. They are the most promising materials for realizing half-metallicity at room temperature owing to their high Curie temperature. We demonstrate a huge tunnel magnetoresistance effect in a magnetic tunnel junction using a Co(2)MnSi Heusler alloy electrode. This result proves high spin polarization of the Heusler alloy. We also demonstrate a small magnetic damping constant in Co(2)FeAl epitaxial film. The very high spin polarization and small magnetic constant of Heusler alloys will be a great advantage for future spintronic device applications.