Dilatometric shrinkage data was utilized to study the sintering kinetics of the in-house synthesized nano-crystalline 3-mol% yttria-samaria codoped tetragonal zirconia polycrystal (TZP) ceramics. The objective was to determine activation energy (Q) of sintering and the sintering mechanism (n) relevant to the initial stage of sintering. The product of activation energy and sintering parameter, i.e., ‘‘nQ’’ was calculated from the shrinkage data acquired from the constant rate of heating experiment. The apparent activation energy of sintering (Q) was calculated using modified-‘‘Dorn’’ method. Modified Johnson’s equation was used to determine value of ‘‘n’’ using the activation energy obtained from the Dorn method. Stepwise isothermal dilatometry technique was utilized as an independent method to determine the ‘‘n’’ value. The activation energy of sintering was in the range of 400–525 kJ mol^-1 and found to be dependent on the dopant concentration. The value of ‘‘n’’ was found to be ~ 0.33 for both 3 mol% yttria-doped (3Y-TZP) and yttriasamaria codoped (3(Y,S)-TZP) TZP, whereas for 3 mol% samaria-doped tetragonal zirconia (3S-TZP), the value of ‘‘n’’ was ~ 0.40. From the obtained ‘‘n’’ values, it may be concluded that grain boundary diffusion (GBD) was the dominant sintering mechanism in 3Y-TZP and 3(Y,S)-TZP, whereas an intermediate of GBD and volume diffusion influences the initial sintering stage in the 3S-TZP.