Tape casting was a new type of low temperature co-fired ceramic (LTCC) forming process, the key to which was the formation of slurry. Suspensions consisting of boronsilicate glass/Al2O3 powders and organic solvent system were studied, in addition, the effect of solid content and mixing time on the property were also investigated. The results indicated that the optimized parameters of the slurry are 55 wt. % boronsilicate glass/Al2O3 composites powders, the three azeotropic solvents (Ethanol/ Dimethylbenzene/ Dimethylcarbinol=30 wt.%: 10 wt.%: 60 wt.%), 3.0 wt.% dispersant, the ratio of plasticizer to binder(R=0.65), and mixing time (20 hours). The green tape had smooth and homogeneous surfaces without cracks, and the sintered sample had a high relative density.