In this paper, studying the effect of increase the number of SiC nanoparticles atoms on the optimized geometrical parameters, electronic and spectroscopic properties of polyvinyl alcohol. The studied structures are (PVA)(43Atom),(PVA-SiC)(35 Atom) and (PVA-SiC)(51Atom) nanocomposites. The optimization parameters included both bonds and angles. The electronic and structural properties included the (energy gap, cohesive energy, ionization potential, electron affinity, chemical hardness, chemical softness, electronegativity, electrophilicity and density of states) as well as spectral properties, which included IR and UV-Visible. This study uses Gaussian 0.9 program with help of Gaussian View 0.5 using density function theory (DFT) with local spin density approximation B3LYP level and6-31Gbasis sets. The results showed that the number of atoms has a direct impact on all the properties of the molecules studied. The increase of number of atoms are caused changes in spectral of (PVA)which include shift in some bonds and change in the intensities. These changes attributed to interactions of nanoparticles (SiC) with (PVA). Also, from Ultra Violet and Visible spectrum observed that absorption increases by increasing the number of atoms, this is due to the excitations of donor level electrons to the conduction band at these energies. The energy gap of the nanocomposites reduce from 6.8568 eV for (PVA) to5.0715 eV for (PVA-SiC)(35Atom) and 4.5330 eV for (PVA-SiC)(51Atom). The total energies decreases with the increase the number of atoms forming the nanocomposites. The results showed that the nanocomposites can be used for different applications such as: solar cells, diodes, transistors, sensors, electronics gates, electronics devices.