Carbon exerts a significant influence on the microstructure of beryllium ceramics. With the introduction of activated carbon into the composition of the ceramic its microstructure undergoes changes. Even small amounts of carbon (about 0.1%) lead to the development of pores. With increase in carbon concentration there is an increase in the amount of large pores. The distribution of pores over the specimen's cross section is irregular. During sintering some of the fine pores in the peripheral section of the specimens succeed in coalescing, and their density and porosity are the same over the section. Additions of carbon in beryllium ceramics limit the grain growth. The growth of crystals in this case is prevented by pores. Small concentrations of pyrolytic carbon in the compositions lead to a retarding of the growth of BeO crystals, and do not have a significant influence on the density. In the case of the obstructed escape of carbon-containing gases from the thickness of the ceramics during sintering there is a reduction in the impurity ions (e.g. iron) which, in the final account, may lead, on the other hand, to a significant increase in the rate of growth of crystals, and the formation of an irregularly grained structure.