This paper investigates the influence of processing parameters on the dielectric constant of compacted cementitious composites based on ordinary Portland cement and silica particles. A full factorial design was carried out to study the effects of size and shape of silica particles and uniaxial compaction pressures of 10 and 30 MPa on the dielectric constant and the apparent porosity of the composites. Silica particle size and compaction pressure were determined to be significant factors affecting the apparent porosity. The dielectric constant of the cementitious composite is significantly influenced by a combination of particle size, shape and compaction pressure.