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In situ synchrotron X-ray diffraction and diffuse reflectance infrared spectroscopy (DRIFTS) are combined to study the influence of sulfur on the crystallization of pure and Fe-doped titania nano-materials. Using these two tools we have investigated the effect of sulfur on the nucleation and growth processes of the anatase polymorph from amorphous powders and show how the addition of sulfur controls the primary particle size and shape of the materials. As well known, sulfur leads to the stabilization of the oxide particle size against sintering during thermal treatments and here we interpret the physico-chemical basis of such behaviour as an exclusive effect on grain growth kinetics, in turn linked to the dehydration of the surface layers of the materials. In addition this work shows that the presence of sulfur also affects the shape of the anatase particles, favouring the existence of (101)-type surfaces and elongated (along the c crystallographic axis) particles. This combined analysis of how sulfur influences morphological aspects of the anatase phase as it grows provides a basis for understanding of surface and chemical properties of anatase nano-powders that are highly dependent upon particle morphology.