The effect on rheological properties of silica/bismaleimide (BMI)/glass fiber prepregs were investigated, where the silica were surface treated bydifferent coupling agents KH-550, KH-560 and KH-570.The rigidity, coefficient of thermal expansion (CTE) and thermal stability of the copper clad laminate (CCL) made with above prepregs were measured by DMA, TMA and TGA methods.