In this work, we present an extensive investigation of the effect of Al2O3 decoration on the morphological, structural and opto-electronic properties of a porous Si (Sip)/Cr2O3 composite. The Sip layers were prepared by the anodization method. Al2O3 and Cr2O3 thin films were deposited by physical vapour deposition. The morphological and micro-structural properties of Sip/Cr2O3/Al2O3 were studied using the scanning electron microscope, energy dispersive X-ray spectroscopy and X-ray diffraction techniques. It was found that Al2O3 decoration with different concentration strongly affects the Sip/Cr2O3 microstructure mainly at the level of porosity. Variable angle spectroscopic ellipsometry demonstrates a strong correlation between optical constants (n and k) of Sip/Cr2O3/Al2O3 and microstructure properties. Dielectric properties of Sip/Cr2O3/Al2O3 such as electrical conductivity and conduction mechanism were explored using impedance spectroscopy over the temperature interval ranging from 340 to 410°C. A semiconductor to the metallic transition has been observed at high frequency.