Calcium copper titanate (CaCu Ti O , CCTO) powder was mixed with boric oxide (B O ) glassy phase up to 8% by weight to prepare the composite ceramics. The effects of B O incorporation on the microstructures, electric and dielectric properties of CCTO ceramics have been systematically investigated. Adding B O results in both the decrease of the CCTO grain size. These microstructural changes conjointly affect the dielectric constant. In addition, further B O increase leads to its aggregation at grain boundaries. Meanwhile, the B O addition reduces the nonlinear coefficient and influences the breakdown electric field. © Springer Science+Business Media, LLC 2012.