The local atomic structure of TiO2 aerogels calcinated at 450 °C and 550 °C has been studied in comparison with that of well-crystallized TiO2 anatase by the X-ray diffraction (XRD) method and Reverse Monte Carlo (RMC) simulations. The influence of calcination temperature on the crystallographic properties and microstructure of TiO2 aerogels was discussed. The large X-ray line broadening of TiO2 aerogels was due to the small crystallite size and lattice strain. From the traditional Williamson-Hall (W–H) analysis results, it was observed that the strain value decreased but the particle size increased as calcination temperature was increased. The TiO2 anatase sample revealed an average particle size of about 62 nm and a very low strain in the nano-crystallite. The experimental X-ray structure factor was derived from the wide-angle X-ray scattering (WAXS) pattern after suitable data reduction. The partial atomic pair correlation functions gij(r), like the gTiO(r), gOO(r) and gTiTi(r) have been revealed from RMC simulation with a fairly good stability and acceptable statistics. The structure model that best describes both the WAXS data consists of nano-crystalline TiO2 with a highly distorted shell and a strained anatase-like crystalline core. The pre-existence of the anatase like core may be critical to the formation of single-phase nano-crystalline TiO2 anatase in crystallization of highly porous TiO2 aerogels upon heating.