Rare element Tellurium (Te) is known as a nonessential toxic element and its biological function has not been described comprehensively yet. Wide spectrum areas show interest in nanoparticles because of their unusual biological features and use in different commercial products. In this research, tellurium dioxide nanoparticle (TeO2 NP) which is an important material for industrial areas including biomedical applications was analysed on cultured Human Pulmonary Alveolar Epithelial (HPAEpiC) and peripheral blood cells. For this purpose, TeO2 NPs size and content were confirmed and characterized via using X-ray crystallography (XRD) and Scanning Electron Microscope (SEM) techniques. Cell viability was determined by 3-(4, 5-dimethyl-thiazol-2-yl) 2, 5-diphenyltetrazolium bromide (MTT) and Lactate Dehydrogenase (LDH) release assays. Also, TeO2 NPs were investigated on the cell cultures in the aspect of Total Antioxidant Capacity (TAC) and Total Oxidative Stress (TOS) levels. The TAC values did not change but, The TOS values significantly increased for the cell cultures after TeO2 NPs application. According to cell viability assays, 160 mg/l concentration of TeO2 NPs was found to be highly toxic for both cell cultures. In the light of these findings, it could be inferenced that TeO2 NPs is immensely cytotoxic for different cell types and toxicity process might occur through oxidative stress mechanism.