Background. Humans are exposed to nanoparticles from a variety of sources through a broad range of exposure ways since nanomaterials are increasingly used in different productive sectors. Titanium dioxide (TiO2) is enclosed in many consumer products including pharmaceuticals, cosmetics, and foods. TiO2 (E171) is daily ingested as mixed nano- and submicron-sized particles since it is approved as a white pigment in Europe in a variety of food products. Noteworthy, the relevant risk assessment has never been satisfactorily concluded and growing alarms for human hazards deriving from TiO2 exposure are incrementally reported. The objective of the present study was to establish conceivable mechanisms by which nano-sized TiO2 particles affect physiological function of the intestinal epithelium layer. Methods. The well-established Caco-2 cell line differentiated on permeable supports was used as a predictive model of the intestinal barrier due to its ability to naturally differentiate into polarized cells which resemble the intestinal architecture. The resultant system was adopted to investigate changes triggered by TiO2 nanoparticles in monolayer barrier since intestinal epithelial barrier is crucial for the maintenance of physiological function and the prevention of uncontrolled antigens trafficking. Results. Exposure to nanoparticles disrupted the tight junctions-permeability barrier with a prompt effect detectable after 4h incubation time and wide effects on barrier integrity at 24h. Transport and ultrastructural localization of TiO2 nanoparticles were determined by ICP-OES, TEM and ESI/EELS analysis, respectively. Nano-sized particles were efficiently internalized and preferentially entrapped by monolayers. Storage of nanoparticles inside the cells affected enterocytes viability and triggered the production of pro-inflammatory cytokines, including TNF-? and IL-8. Conclusions. Nano-sized TiO2 particles exert detrimental effects on the intestinal epithelium layer.