In order to clarify the formation mechanism of zilconia fine particles produced by spray-pyrolysis, the fine structure with particles is elucidated based on structural analysis of dried particles and decomposed particles. From SEM photograph observation, relatively large hollow spheres appear In particles produced from the concentrated solution with 1 kmol.m(-3) and those from the dilute solution with 0.1 kmol.m(-3) are solid spheres. From structural analysis of the dried and decomposed particles, it is indicated that the dried particles are non-porous with irrespective of the temperature and the concentration. For the dilute solution, the decomposed particles under any temperatures have mesopores. For the concentrated solution, however, the pore radius shifts from the micropore region to the mesopore region with increase in temperature.