This study presents the effect of illumination on main electrical parameters of Schottky barrier diode (SBD). The admittance (capacitance-voltage (C-V) and conductance-voltage (G/omega-V)) characteristics of Au/Zinc acetate doped polyvinyl alcohol (PVA:Zn)/n-Si SBD were investigated in dark and under various illumination intensities. Experimental results demonstrate that the C-V plots give a peak due to the illumination induced interface states or electron-hole pairs at metal/semiconductor (M/S) interface. The C-2-V plots were also drawn to determine main electrical parameters such as doping concentration (N-D), depletion layer width (W-D) and barrier height (Phi(B)(C-V)) of device. In addition, the voltage dependence R-s values were obtained from C-V and G/omega-V data by using Nicollian and Brews method. In order to obtain the real diode capacitance and conductance, the high frequency (1 MHz) C-m and G(m)/w values were corrected for the effect of series resistance. All these observations confirm that both C-V and G/w-V characteristics were strongly affected by illumination.