Titanium dioxide ($TiO_2$) nanoparticle is an important product for nanotechnology because of its high stability, anticorrosion, and photocatalysis. It is also used in cosmetic and skin care products, particularly in sunblocks, where it helps to protect the skin from UV light, especially in the case of nanosized particles (<100 nm). There are extensive concerns on the potential risks of $TiO_2$ nanoparticle to human health and environment. Some forms at least may be genotoxic, photocatalytic, and/or carcinogenic. In this study, we have characterized the physico-chemical properties of commercially available photocatalytic $TiO_2$ nanoparticle and compared to cellular effects in HaCaT Cells with or without photoactivation. The present study has shown that $TiO_2$ nanoparticles are cytotoxic to HaCaT cells even in the absence of photoactivation. This effect became more pronounced in the simultaneous irradiation of UVA dependent on photocatalytic potential of $TiO_2$ nanoparticle. We also found that the cytotoxicity and oxidative stress of $TiO_2$ nanoparticles strongly depends on physico-chemical properties including structure (anantase, rutile, or mixture) or photocatalytic potency of $TiO_2$ nanoparticles.