Abstract: The existence of pores is one of the most important factors affecting the performance of transparent laser ceramics. In order to analyze the influence of pore size and porosity on laser performance of transparent ceramics, zeroth-order lognormal distributions (ZOLDs) have been used to describe the pore size distributions, and Mie scattering theories combined with related solid-state laser theories have been used to illustrate the effect of pore scattering on transmittance, laser slope efficiency and laser threshold of transparent ceramics. The results show that transmittance and laser slope efficiency are significantly influenced by porosity, i.e., larger porosity leads to lower transmittance and slope efficiency at given pore size distribution; transmittance and slope efficiency decrease with increasing central pore size, and slope efficiency drops sharply when pore radii are between 0.1 and 0.3 m. Moreover, the larger the pore sizes are, the sharper the laser threshold rises. In practical applications, improving fabrication technology to control pore size is of great importance to improve the laser performance of transparent ceramics.