Aluminum-nickel nano-alloys were prepared by successive evaporation of nickel and aluminum ultra-thin films on silicon and glass substrates at room temperature. Alloying was obtained through the spontaneous intermixing of the ultra-thin layers at room temperature. The shift in the X-ray photoelectron spectroscopy (XPS) peaks of the pure metals indicated the alloying process in the films. Using spectroscopic ellipsometry from the UV to near infrared spectral range, the optical properties of these films were investigated. The effective pseudo-dielectric functions obtained by direct inversion of the ellipsometry spectra reveled a surface plasmon resonance at 364 nm in the prepared alloys. The resonance peak was pronounced for the pure nickel films and it did not suffer any spectral shift when the films were alloyed with aluminum. Interpretations of this behavior is presented.