Zirconium dioxide (ZrO2) nanoparticles were heated at 1200 K in a transmission electron microscope, and their surfaces were observed in situ via lattice imaging. The nanoparticles exhibited well-defined crystal habits while fluctuating the surface terrace structures. The stable surfaces and ridges were inferred from the fluctuation of the terraces, leading to the construction of the three-dimensional surface structures at 1200 K. By contrast, after the specimen cooled to room temperature, the surface fluctuation of the nanoparticles stopped and the crystal habit disappeared, implying that the crystal habit was maintained because of atomic diffusion during the surface fluctuation.