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The effects of alkali oxides (Na2O and K2O) addition on both the sintering behavior and dielectric properties of Ca-Al-B-Si-O glass/Al2O3 composites were investigated by Fourier transform infrared spectroscopy (FTIR),differential scanning calorimeter (DSC),X-ray diffractometry (XRD) and scanning electron microscopy (SEM).The results show that the increasing amount of alkali oxides in the glass causes the decrease of [SiO4],which results in the decrease of the continuity of glass network,and leads to the decrease of the softening temperature Tf of the samples and the increasing trend of crystallization.And that deduces corresponding rise of densification,dielectric constant,dielectric loss of the low temperature co-fired ceramic (LTCC) materials and the decrease of its thermal conductivity.By contrast,the borosilicate glass/Al2O3 composites with 1.5％ (mass fraction) alkali oxides sintered at 875 ℃ for 30 min exhibit better properties of a bulk density of 2.79 g/cm3,a porosity of 0.48％,a λ value of 2.28 W/(m-K),a εr value of 7.82 and a tanδ value of 9.1×10-4 (measured at 10 MHz).