Si/PVA-PEG polymer nanocomposites wereprepared by solvent casting method. XRD studies revealed the encapsulation of silicon in polymer matrix. Further crystalline behaviour of silicon in the polymer nanocomposites has been investigated. The size and morphological structure have been analysed with SEM. SEM showed the formation of homogeneous between PVA and PEG. FTIR confirmed the presence of silicon and various vibrational bonding natures. Band gap and refractive index of composites have been calculated from optical studies. Z-Scan analysis has been carried out at 532 nm which reveals optical non linearity of Si/PVA-PEG.