Large surface area coatings of oxygen deficient nanocrystalline TiO₂ are of immense use in antifogging mirrors and self cleaning windows. Spray pyrolysis is a simple versatile technique to coat relatively large surface area. A clear understanding of effect of substrate temperature on the coating morphology, structure, composition and optical properties is essential to produce coatings of desired properties. Oxygen deficient nanocrystalline anatase–TiO₂ thin films were synthesized on Si(1 0 0), quartz and glass substrates at 300–550 °C. Well defined platelets like nanograins standing on their edge were obtained at 500 °C. The crystallites were found to be of ˜12 nm thickness and ˜30 nm major diameter. The secondary ion mass pectrometric studies of the films revealed uniform distribution of titanium and oxygen across the thickness of the film up to the film–substrate interface. Presence of lower valent Ti ions and oxygen vacancies were confirmed from XPS studies. The indirect and direct band gap values evaluated from the Tauc plot for films synthesized at 500 8C are 3.3 and 3.62 eV respectively.