A unique porous YSZ surface morphology is observed and reported, for the first time, during the sintering of YSZ-MnO2 composite. The porous YSZ morphology largely depends on YSZ/MnO2 ratio and sintering temperature, time, and atmosphere. The structural evolution is hypothesized to be due to the presence of Mn especially related to Mn diffusion, dissolution, precipitation, and evaporation. A series of experiments were designed and conducted to investigate the porous morphology formation with emphasis on performing quench experiments that showed the initiation of porous surface evolution during cooling. Computational thermodynamics has been applied to investigate the role of Mn on the surface porosity formation.