Nanoparticles (NPs) can interact with the immune system in several ways, which can either enhance or suppress the functions, depending on their characteristics and composition. Though widely used in different biomedical applications, not much is known about the immunomodulatory effects of NPs on human cell lines. In this work, the immunomodulatory effects of titanium dioxide (TiO2) nanoparticles on human monocytic leukemia (THP-1) and human mast (HMC-1) cell lines were studied in a dose-dependent manner. TiO2 NPs of different molar concentrations were synthesized by a simple sol-gel method and analyzed by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) technique, UV-vis spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS) and Zeta Potential. The cell viability of THP-1 cells treated with TiO2 NPs was significantly reduced at higher doses as observed by MTT assay. The expressions of Pro and anti-inflammatory cytokines on THP-1 and HMC-1 cells using TiO2 NPs were studied using ELISA method. The results suggested that the secretion of cytokines (IL-6 and IL-10) on human cell lines greatly depended on the concentration of TiO2 NPs. Lower concentrations of TiO2 NPs exhibited immunomodulatory effects by inducing inflammatory responses on the treated human cell lines.