This paper presents ceramic multi-layer substrates for mobile communication using alumina-glass composite ceramics and co-fired copper conductors. Electrical characteristics in GHz frequencies of the substrate, copper conductor, transmission line, via hole and coupling between the striplines were evaluated. The results showed that the ceramic multi-layer substrate had good electrical characteristics enough for GHz-band applications. Using the ceramic multi-layer substrates, one can drastically reduce the size of RF circuit boards for mobile communication equipment.