Au/TiO₂ core-shell structure nanoparticles were synthesized by sol-pel process, and the morphology and crystallinity of TiO₂ shell were investigated by TEM and UV-vis absorption spectrometer. Au/TriO₂ core-shell structure nanopanticle could be prepared by the hydrolysis of TOAA (titanium oxide acethylacetonatc) in gold sol ethanol solution with water. The thickness ui TiO₂ shell on the surface of gold particles was about 1 ㎚. To investigate the crystallinity of TiO₂ shell, UV light with 254 ㎚ and radioactive ray of ^(60)Co uerr imdiuted on the TiO₂-coated gold sol ethanol solution. The surface plasmon band of gold nanopmicles appeared only when the radioactive ray was irrdiated on the TiO₂-coated gold sol ethanol solution. From these results, it was found that the TiO₂ shell was amorphous end the MUA (mercaptoundecanoic acid) layer on the Au particle for its dispersion in ethanol did not act as an obstacle to disturb the movement of electrons onto the surface of Au panicles.