In recent years, 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) doped with copper oxide has obtained increasing interest due to its enhanced superplastisity and good potential in tribological applications. In this work, the effect of addition of small amounts (0.8 mol%) of copper oxide on the sintering behavior of 3Y-TZP was studied using a dilatometer and high-temperature X-ray diffraction (XRD). A qualitative sintering model was established based on several reactions during sintering as indicated by thermal analysis and XRD. Some of these reactions remarkably retard densification and consequently result in low final density (86%) of the sample sintered at 1400 degrees C in air. The reaction between molten Cu2O and yttria as segregated to the Y-TZP grain boundaries at around 1180 degrees C leads to the depletion of yttria from Y-TZP grains, which results in the formation of monoclinic phase during cooting. A relatively higher oxygen partial pressure can inhibit the dissociation of CuO to Cu2O. This inhibition in dissociation is one of the reasons why a dense (> 96%) 0.8 mol% CuO-doped 3Y-TZP ceramic can be obtained after sintering at 1400 degrees C in flowing oxygen.