Microwave-assisted synthesis represents a valuable improvement in the domains of molecular and organic chemistry and was recently extended to inorganic and materials chemistry. A comparison of titanium dioxide nanoparticles synthesised in aqueous solution prepared in a microwave or a conventional oven is presented here. More precisely, three different protocols were used in order to determine the impact of the heating mode on the final product in terms of crystalline structure, particle size and morphology. Therefore, the resultant powders were analysed by Raman spectroscopy as well as X-ray and electron diffraction and transmission electron microscopy. The results show that microwave treatment significantly reduces the heating time and generally produces smaller nanoparticles. The rutile/anatase/brookite phase distribution is also modified by the heating mode in certain protocols up to the formation of a pure anatase phase, for instance. The impact of microwaves on the solvent and on the inorganic precursors has been demonstrated. A photocatalytic test and time-resolved microwave conductivity experiments were performed on rather similar samples prepared with the two heating modes in order to probe the improvement of the crystalline quality and its consequences on the photocatalytic activity of the TiO2 material.