The mechanical behavior of nanostructured spherical submicrometer titania particles was studied by insitu uniaxial compression experiments in the scanning and transmission electron microscope (SEM and TEM). Mesoporous and amorphous titania particles were prepared by a wet chemical sol-gel approach. To obtain nanocrystalline (nc) single-phase anatase and rutile particles the amorphous particles were crystallized by high-temperature annealing. For each sample the deformation behavior of at least 50 particles was investigated by insitu compression experiments in the SEM. In all cases an elastic - predominantly plastic deformation behavior accompanied by crack initiation at exceptionally high engineering strain values of several percent were observed. Crack propagation presumably along grain boundaries and a Weibull distributed fracture stress was shown for all nc particles. Complementary insitu TEM experiments and ex situ analysis of focused ion beam prepared particle cross-sections were carried out to identify the underlying deformation mechanisms. Grain rotations and grain sliding are observed for nc anatase particles during insitu compression and are further identified to be linked to a densification of the mesoporous particle structure. Our dedicated preparation and quantitative insitu characterization methodology provides an excellent basis for a better understanding of the mechanical behavior of advanced ceramics.