Nanoparticles (NPs) are widely used in food, and analysis of their potential gastrointestinal toxicity is necessary. The present study was designed to determine the effects of silica dioxide (SiO 2 ), titanium dioxide (TiO 2 ), and zinc oxide (ZnO) NPs on cultured THP-1 monocyte-derived macrophages and human epithelial colorectal adenocarcinoma (Caco-2) cells. Exposure to ZnO NPs for 24 h increased the production of redox response species (ROS) and reduced cell viability in a dose-dependent manner in THP-1 macrophages and Caco-2 cells. Although TiO 2 and SiO 2 NPs induced oxidative stress, they showed no apparent cytotoxicity against both cell types. The effects of functionalized SiO 2 NPs on undifferentiated and differentiated Caco-2 cells were investigated using fluorescently labeled SiO 2 NPs with neutral, positive, or negative surface charge. Exposure of both types of cells to the three kinds of SiO 2 NPs significantly increased their interaction in a dose-dependent manner. The largest interaction with both types of cells was noted with exposure to more negatively surface-charged SiO 2 NPs. Exposure to either positively or negatively, but not neutrally, surface-charged SiO 2 NPs increased NO levels in differentiated Caco-2 cells. Exposure of differentiated Caco-2 cells to positively or negatively surface-charged SiO 2 NPs also upregulated interleukin-8 expression. We conclude that functionalized surface-charged SiO 2 NPs can induce pro-inflammatory responses but are noncytotoxic.