We have investigated to immobilize non close-packed silica colloidal crystalline arrays in aqueous dispersion with hydrophilic polyethylene glycol acrylate polymer and to examine microstructures of the immobilized colloidal crystalline array by using the angle-resolved reflection spectroscopy and scanning probe spectroscopy (SPM). Above nine of ethylene glycol chain length and below 10 wt % of monomer concentration in the dispersion, the structure of the three-dimensional array in the aqueous dispersion is kept with immobilizing process. Angle-resolved reflection spectra indicate refractive index increase, and interplaner spacing decreases with the increase of the particle volume fraction. The SPM phase images proved the crystal structure of the immobilized colloidal crystalline array of face-centered cubic (fcc) structure. The interplaner spacings of the crystalline structure derived from angle-resolved reflection spectra agree with those derived from SPM topographic images. We have demonstrated the microstructure of the polymer-immobilized colloidal crystalline array directly and open the possibility of tuning the microstructure of colloidal crystalline array for photonic crystal. (c) 2006 Wiley Periodicals, Inc.