Titanium dioxide TiO₂ in the anatase form and nanosize crystals is well known for its photoactivity. The electron–hole pairs produced in the TiO₂ as a result of irradiation by UV light (sunlight) have a sufficiently high redox potential to produce hydroxyl radicals in the presence of H₂O that can oxidise organic compounds to CO₂. Thus TiO₂ sees applications in water and air purification and in self-cleaning systems. For practical purposes in many applications, it is necessary to bind the TiO₂ nanocrystals onto a substrate while at the same time ensuring maximum exposure of the TiO₂ surface to the UV light (sunlight) and the medium containing the organic material to be oxidised. Here we report the development and characterisation of a novel nano-structured calcium silicate–TiO₂ composite material comprising a proprietary nano-structured calcium silicate host material which has an open framework structure and a large surface area to which anatase TiO₂ has been attached during synthesis. The composite material has been characterised and tested in the photocatalytic degradation of phenolphthalein. The highest photocatalytic activity was observed when the calcium silicate–TiO₂ composite material contained discrete TiO₂ particles of about 30–100 nm in size on the surface of the silicate host.