The preparation of Nd- and Ce-doped UO2 microspheres was studied, applying the sol-gel method via internal gelation (IG). Un-doped, and Ln-doped ammonium diuranate (ADU) gels with Ln molar metal fractions up to 30 mol% and an increment of 5 mol% were prepared (Ln = Nd, Ce). The dried gels were characterised using optical microscopy (OM) and X-ray powder diffraction (XRD), additionally thermogravimetric differential scanning calorimetry (TG-DSC) measurements were carried out on un-doped microspheres and particles containing 10 mol% dopant. The ADU matrix of the dried particles is converted during a thermal treatment via U3O8 into a UO2 matrix, which was carried out by a calcination in air (900 °C, 1 h) and a sintering in a mixture of Ar:H2 and Ar:O2, corresponding to an oxygen potential of about −420 kJ mol−1 , at 1600 °C for 10 h. Calcined intermediates of the un-doped particle batch, and particles each doped with 10 mol% Nd and Ce, were analysed by XRD. Sintered products of all compositions were also characterised by XRD, and additionally via scanning electron microscopy (SEM). The micropraphs, XRD patterns, TG-DSC results and all data associated with the particle fabrication and characterisation, are part of this dataset.