Abstract CdS nanoparticles with size of 2.5±0.4 nm were prepared by using well-known reverse micelle methods. The CdS particles were characterized with ultraviolet and visible (UV–vis) absorption spectroscopy, transmission electron microscopy (TEM), energy-disperse X-ray analysis (EDX), Fourier transform infrared (FT-IR), and X-ray diffraction (XRD). Twisted nematic liquid crystal display (TN-LCD) devices, doped with various amount of CdS nanoparticles, were studied for the first time. The results showed that electro-optic characteristics were featured by a frequency modulation. As the amount of dopant increased, a wider frequency response was achieved. Interestingly, the driving voltage of TN-LCD decreased as 4′-pentylbiphenyl-4-carbonitrile (4′-pentyl-4-cyanobiphenyl, 5CB) was doped with CdS nanoparticles.