The quasi-static confined uniaxial compaction of granular alumina and boron carbide was studied, and the effect of triaxial stress on the materials as a function of increasing particle size was observed. The average particle sizes studied for granular alumina were 170 +/- 63, 230 +/- 55, 330 +/- 67, and 450 +/- 83 mu m. The average particle size studied for granular boron carbide were 170 +/- 40, 190 +/- 34, 320 +/- 59, and 470 +/- 90 mu m. The material response at hydrostatic pressure as a function of porosity, the bulk modulus as a function of hydrostatic pressure, and the transmission ratio as a function of applied load was evaluated for increasing particle size. For alumina, the increase in particle size resulted in an increase in strength for a fixed porosity, the bulk modulus of this material did not show clear particle size-dependent trends, and the transmission ratio increased with increase in particle size. Conversely, for granular boron carbide, the hydrostatic pressure-porosity curve shifted to the right with increasing particle size, the change in bulk modulus increased with increasing particle size, and no clear particle size-dependent trends were observed when looking at the transmission ratio during the experiment. Post-experiment scanning electron microscopy revealed that alumina powder fragmented from elongated shapes to block-like structures, while boron carbide powder appeared more circular before the experiments and fragmented into smaller comminuted pieces. This paper discusses the implication of the work in the context of the limited experimental data in the field and the modeling of granular advanced ceramics behavior.