A mixture system of MO-SiO2 (M: Ca, Sr, Ba) glass and Al2O3 crystalline powder has been investigated as a substrate material for low temperature co-fired ceramics (LTCC). This type of glass-ceramic mixture is known to be crystallized during the sintering process. We found that the adhesion strength of external electrode was strongly related with sintering condition. Crystallization behavior was monitored by means of powder X-ray diffraction (XRD). The microstructure of sintered body after electroless plating was examined by Scanning Electron Microscopy (SEM). It was observed that the degree of crystallization was strongly affected by sintering condition. We focused ourselves on elucidating the relationship between the degree of crystallization and the adhesion strength of external electrode that was made by means of electroless plating.