The defects of compaction induced during the pressing of powders frequently act as microcracks which initiate the brittle fracture of ceramics. A vibratory assistance to the compaction reduces the scattering of size and limits the severity of flaws, which leads to an increase of the Weibull modulus. The study of the compaction of different ceramic powders shows that the vibrations mainly influence the initial rearrangement of agglomerates.