In this paper, doping liquid materials to enhance the electro-optical (EO) properties of twisted nematic liquid crystals (NLCs) was presented. Two polycyclic aromatic hydrocarbon (PAH) liquids, toluene and 1-methylnaphthalene, were chosen as dopants in order to lower the driving voltage and response time of the NLCs. We find that the main reason of this phenomenon is due to a large amount of reduction in the rotational viscosity of PAH liquids doped NLCs. Without the drawbacks of aggregation that the solid nanoparticles could have, the method of doping liquids provides a more reliable choice for applications in various LC display systems.