Transparent self-cleaning nanocoatings made up by titanium dioxide (TiO2) colloidal suspensions applied by spray on limestone have been tested in order to assess their influence on stone substrates and their photocatalytic activity. The deposition of TiO2 nanoparticles did not lead to damaging effects on substrate, on the other hand self-cleaning efficiency was evident. Furthermore, treated stones have been artificially aged to evaluate their behaviour over time and their possible lifespan. The efficiency of TiO2 nanotreatments seems durable over time, but further investigations are necessary to establish the real resistance of TiO2 on stones.