In this research, cadmium sulfide nanostructures have been prepared by an ultrasound-assisted method in presence of polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP) as capping agents. The effects of two different capping agents on the structural and optical properties of cadmium sulfide nanostructures have been investigated by X-ray diffraction (XRD), UV-Vis spectroscopy, scanning electron microscopy (SEM) and Fourier transform Infrared (FT-IR) spectroscopy. The XRD patterns show the high purity of samples. The mean crystal's sizes have been estimated by Debye-Sherrer equation and results show the mean crystallite size is decreasing with increase capping agent concentrations. UV-Vis spectroscopy results show a shift in the peaks and broadening with the PVA and PVP increasing. The broadening of the absorbance spectrum with increasing in capping agent concentrations is due to the quantum confinement of nanostructures. The band gap of prepared samples has been estimated by Tauc equation and graph and results show that the band gaps of samples are increasing with increase in the capping agent's concentration. The SEM images show the distribution of the uncapped sample is different from capped samples. FT-IR spectroscopy results show by increasing of capping agent concentration the energy between the functional group is changed and some peaks show a slight shift.