The aim of this work was the fabrication of mesoporous silica nanoparticles functionalized with thermochromic dye for further incorporation onto textiles. The nanosilicas were prepared under alkaline conditions in the presence of the surfactant hexadecyltrimethylammonium chloride and functionalized with the organosilane dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (C18-NTMS). The dye was incorporated onto the mesoporous silica nanoparticles by two different methods: co-condensation and post-grafting, i.e. by adding the dye during or after the synthesis of the nanosilica, respectively. The morphology, particle and pore size, chemical composition, and textural properties of the silica nanoparticles were characterized by scanning electron microscopy (SEM), dynamic light scattering, N-2 adsorption isotherms at -196 A degrees C, Fourier transform infrared spectroscopy and thermogravimetry. The silica nanoparticles prepared with and without dye presented spherical shape (by SEM) and particle size ranging from 15 to 40 nm. The infrared spectra revealed the characteristic bands of silica and organosilane (in the cases where it was used). The prepared materials presented colour change when submitted to different conditions. The thermochromic dye-functionalized nanosilicas were efficiently immobilized into cotton fabric and tests were performed to verify the washing fastness. After washing, a slight decrease on the amount of silica was noticed, but much of it remained on the textile. The functionalized textiles presented a colour change within different conditions.