Based on Effective Mass Approximation (EMA) and Hyperbolic Band Model (HBM), the effect of quantum confinement upon the energy band gap and reduced effective masses of CdSe nanoparticles has been examined. The size of nanoparticles were used from experimental data, such as X-ray diffraction (XRD), Scanning and transmission electron microscopy and the band gap also derived from optical spectroscopy. Also preparation of CdSe nanocrystals was achieved via ultrasound- assisted method. X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Uv-visible spectroscopy were used to characterize the structural and optical properties of as-prepared nanostructures. The experimental results showed that the as-prepared CdSe nanostructures are formed with very small nanometer size, which showed a blue shift of about 0.4eV in energy gap. Theoretical study showed that the value of the reduced effective mass of charge carriers in quantum sized CdSe materials differs from its bulk crystal. The comparative analyses and the main reasons of the changes in reduced effective mass value in the case of CdSe nanoparticles are briefly discussed.