Two zinc oxide nanoparticles (ZnO NPs) with different physicochemical properties (ZnO(α) and ZnO(Σ)) were examined in THP-1 cells to investigate their effects on cellular immunomodulation and cytotoxicity. It was considered that there was a potency shift that is associated with cytotoxicity and physicochemical properties, in immunomodulatory activities in THP-1 cells between ZnO NPs.