The aim of this work was to design plates and millireactors made of polypropylene on the FFF 3D printer. Then cover the plates and channels of the millireactor with a sensor coating that is previously prepared using the sol-gel method. The sensor films were prepared using tetraethoxysilane, TEOS, and phenyltrimethoxysilane, FTMS as a precursor for the sol-gel method, ethanol as a solvent, methyl red as a pH indicator, and hydrochloric acid, HCl, as a reaction catalyst. The plates were successfully made on a 3D printer, and the sensors on the surface of the plates showed a response, the color of the sensor films changed. The millireactors also showed a response, there was a change in the color of the sensor films in the channels of the millireactor, to the pH value. The change in color of the sensor films was not visible to the naked eye, but a trend of RGB values to pH was observed using the RGB color analysis software. Melting enthalpy and melting temperature are higher with polypropylene that was in the form of granules compared to the polypropylene produced by BASF that was used for 3D printing of plates and millireactors, which is in the form of filaments. By measuring the contact angle, it was concluded that the hydrophobicity of the plates decreases with the use of sensor films. FTIR analysis of plates with and without sensor film confirmed the presence of polypropylene functional groups. By analyzing the plates with the sensor film, the functional groups of the silane precursors that were used to make the films were found.