In this study, we have investigated ultraviolet (UV) illumination effect on electro-optical and dielectric properties of varying concentration of CdSeS/ZnS semiconductor quantum-dot-doped 5CB nematic liquid crystal. Dielectric measurements were made from 10 kHz to 10 MHz frequency ranges in dark and under UV-illumination conditions. Electro-optical measurements were also performed with a voltage-dependence light transmission system at 10 kHz frequency in dark and under UV-illumination conditions. Significant physical parameters such as relaxation frequency (fR), real and imaginary components of complex dielectric permittivity (e′ and e′′), and threshold voltage (Vth) values were obtained from experimental results. Results show that UV-illumination effects cause considerable improvements on electro-optical and dielectric characteristic of investigated samples.