The main purpose of this thesis is to investigate the electro-optical properties of insulated nanoparticle-doped 90。 twisted nematic liquid crystal cells. We measure their transmittance curve and transient current. The experimental results show that a minute addition of insulating nanoparticles such as , , and lead to a reduction of the ion concentration in the cells so as to reduce the transient current and the threshold voltage. Simultaneously, the voltage holding ratio can be held higher than 95% which is a superior feature compared to the carbon nanotube doped cells. These experimental results are almost independent of the type of the nanoparticle. We speculate that the reduction of the ion concentration is due to the ion trapping by the polarized dielectric nanoparticles under an external electric field.