Dependence of the freeze-drying process condition on microstructure of porous W and pore formation mechanism were studied. Camphene slurries with $WO_3$ contents of 10 vol% were prepared by milling at $50^{circ}C$ with a small amount of dispersant. Freezing of a slurry was done in Teflon cylinder attached to a copper bottom plate cooled at $-25^{circ}C$. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was hydrogen-reduced at $800^{circ}C$ for 30 min, and sintered in the furnace at $900^{circ}C$ for 1 h. After heat treatment in hydrogen atmosphere, $WO_3$ powders were completely converted to metallic W without any reaction phases. The sintered samples showed large pores with the size of about $70{mu}m$ which were aligned parallel to the camphene growth direction. Also, the internal wall of large pores and near bottom part of specimen had relatively small pores with dendritic structure due to the growth of camphene dendrite depending on the degree of nucleation and powder rearrangement in the slurry.