Thermal shock behavior of porous ceramic nozzles with various pore sizes for continuous casting process of steel was investigated in terms of physical properties and microstucture. Porous nozzle samples with a composition of $Al_2O_3$-$SiO_2$-$ZrO_2$ were fabricatedby adding various sizes of graphite as the pore forming agent. As the graphite size increased from 45~75 to 150~180 ${mu}m$, both the resulting pore size and the flexural strength also increased. A thermal shock test was carried out at temperatures (${Delta}$T) of 600, 700, 800, and 900$^{circ}C$. Microstructure analysis revealed a small number of cracks on the sample with the largest mean pore size of 22.32 ${mu}m$. In addition, increasing the pore size led to a smaller decrease in both pressure drop and elastic modulus. In conclusion, controlling the pore size can enhance thermal shock behavior.