The spontaneous vertical alignment of the mixtures consisting of nematic liquid crystals (LCs) and nanoparticles and its application to hybrid-aligned nematic (HAN) modes were investigated. The LC directors were aligned perpendicular to the nontreated indium-tin-oxide surface by adding the nanoparticles. Therefore, we fabricated a nanoparticle-filled HAN LC cell without using the vertical alignment layer. The electro-optical properties of nanoparticle-filled HAN cells are very similar to those of conventional HAN cells containing vertical alignment layers. The method of nanoparticle-induced vertical alignment is suitable for fabricating a flexible display due to the reduction of high temperature process of alignment layers.