The sintering behavior of 3 mol% Y2O3-doped zirconia powders with and without a small amount of GeO2 was investigated to clarify the effect of GeO2 addition on the initial sintering stage. The shrinkage of powder compact was measured under constant rates of heating (CRH). The sintering rate was accelerated by GeO2 addition, and increased with increasing GeO2 content. The mechanism, apparent activation energy (nQ), and apparent frequency factor (beta(n)(0)) of diffusion at the initial sintering stage were estimated using the sintering-rate equations that are applicable to the CRH data. The sintering mechanism changed from grain-boundary (GBD) to volume diffusions (VD) by GeO2 addition, and both nQ and beta(n)(0) of diffusion increased with increasing GeO2 content. It is, therefore, concluded that the enhanced sintering mechanism by GeO2 addition is explained by the GBD-->VD change and increases in both nQ and beta(n)(0) of diffusion at the initial sintering stage.