The effect of specific surface area on the growth and the porosity of oxide ceramic superconductor YBCO single domain are investigated. The enhancement of growth depth depends on the large specific surface area σ. When the specific surface area σ is more than the critical value 200mm2/g, the YBCO single domain is full-growth in the sample of size Ф20mm×18mm. It reveals that a large specific surface area providing an effective tunnel of oxygen diffusion for the crystal growth. On the other hand, this tunnel makes oxygen gas emitting out resulting in porosity diameter decreased. The mean porosity diameter is observed as 5μm in hole sample smaller than 80μm in plain sample. The porosity distribution is calculated as 1/(100μm)2 in plain sample and 8/(10μm)2 in hole sample.