Ultrafast high-temperature sintering (UHS) of 3YSZ (yttria-stabilized zirconia) was compared with conventional sintering. UHS allows ultra-rapid consolidation of YSZ nanopowders (<30 s) with a densification pathway different from conventional sintering, resulting in a grain size reduction by more than 60% at a fixed density level. The electric field plays a minor role in sintering, microstructure evolution, and properties. UHS does not affect the hardness and electrochemical properties of the sintered bodies. While similarities exist between UHS and flash-related techniques in terms of accelerated densification and microstructure, the final properties of UHS YSZ are more similar to conventional sintering. UHS enables rapid densification with a processing temperature reduction of over 200°C compared to conventional heating. The microstructure of UHS samples shows a finer grain size and smaller, less coordinated pores compared to conventionally sintered samples. The hardness of UHS and conventionally sintered materials increases with density, and the electrochemical properties of UHS and conventional sintered samples are similar. The grain boundary properties measured by EIS are similar for both UHS and conventional sintering, with an electrochemical grain boundary thickness of approximately 18 nm. The results suggest that the observed modified electrochemical and mechanical properties are not solely due to ultra-rapid heating but also to the pore architecture and microstructure. The study concludes that UHS allows rapid densification of 3YSZ nanopowders with a relatively homogeneous microstructure, and the properties of UHS and conventionally sintered materials are similar in terms of electrochemical response and hardness.Ultrafast high-temperature sintering (UHS) of 3YSZ (yttria-stabilized zirconia) was compared with conventional sintering. UHS allows ultra-rapid consolidation of YSZ nanopowders (<30 s) with a densification pathway different from conventional sintering, resulting in a grain size reduction by more than 60% at a fixed density level. The electric field plays a minor role in sintering, microstructure evolution, and properties. UHS does not affect the hardness and electrochemical properties of the sintered bodies. While similarities exist between UHS and flash-related techniques in terms of accelerated densification and microstructure, the final properties of UHS YSZ are more similar to conventional sintering. UHS enables rapid densification with a processing temperature reduction of over 200°C compared to conventional heating. The microstructure of UHS samples shows a finer grain size and smaller, less coordinated pores compared to conventionally sintered samples. The hardness of UHS and conventionally sintered materials increases with density, and the electrochemical properties of UHS and conventional sintered samples are similar. The grain boundary properties measured by EIS are similar for both UHS and conventional sintering, with an electrochemical grain boundary thickness of approximately 18 nm. The results suggest that the observed modified electrochemical and mechanical properties are not solely due to ultra-rapid heating but also to the pore architecture and microstructure. The study concludes that UHS allows rapid densification of 3YSZ nanopowders with a relatively homogeneous microstructure, and the properties of UHS and conventionally sintered materials are similar in terms of electrochemical response and hardness.