ThO2 powder was obtained by precipitating thorium oxalate from thorium nitrate solution using oxalic acid in the presence of ultrasound and then calcinating the precipitate. ThO2 and 0.25 mol% V2O5, 0.25 mol% Ta2O5 and 0.25 mol% Nb2O5 separately mixed then pressed into cylindrical pellets. The green pellets were sintered at 1400 and 1700 T under Ar-10% H-2 atmosphere. Sintered densities of pellets were determined and microstructural observations carried out. The results showed that Ta2O5 and Nb2O5 doped ThO2 pellets had higher densities than V2O5 doped ThO2 pellets after sintering at 1400 and 1700degreesC. Ta2O5 and Nb2O5 doped ThO2 pellets reached a density of 97% TD after sintering at 1700 degreesC. Microstructural observations showed that V2O5 doped thoria pellets after sintering at 1700degreesC had average grain size of 15 mum while it was 32 and 30 mum for the Nb2O5 and Ta2O5 doped ThO2 pellets, respectively.