The shrinkage behaviour of ThO 2 , ThO 2 -30%PuO 2 , ThO 2 -50%PuO 2 and ThO 2 -75%PuO 2 pellets has been studied using a dilatometer in inert (Ar) and reducing atmospheres (Ar-8%H 2 ). The effects of dopants of CaO and Nb 2 O 5 on shrinkage of the oxides of the above Pu/(Pu+Th) ratios were also studied. Out of the two dopants studied, CaO was found to give larger shrinkage for all the Pu/(Pu+Th) ratios covered in this study. It was also found that the shrinkage was marginally larger in Ar-8%H 2 than in Ar atmosphere. Addition of PuO 2 to ThO 2 enhanced sintering. This was found to be true for both the dopants. During the sintering of ThO 2 , a prominent peak was observed in the shrinkage curve at around 100-300 o C. This peak was attributed to the pressure increase of the trapped gases which subsequently release at high temperatures.