Abstract: NH2-SBA-15 was prepared by amino group functionalization to mesoporous silica SBA-15. Then a series of polybenzoxazole/SBA-15 (PBO/SBA- 15) composites with different SBA-15 contents were prepared via solution polycondensation. The structure, morphology, thermal property and electromagnetic properties of composites were characterized by FT-IR, SEM, TG and VNA, respectively. And the effect of SBA-15 on the dielectric loss of PBO/SBA-15 composites was studied. Results demonstrate that NH2-SBA-15 could disperse in PBO matrix uniformly. And the prepared PBO/SBA-15 composites still maintain an outstanding thermal stability when the mass fraction of SBA-15 is below 8%. The introduced SBA-15 could reduce the complex permittivity and dielectric loss tangent of PBO and result in a reduced dielectric storage and loss performance of PBO/SBA-15 composites to electromagnetic wave energy, making PBO/SBA-15 composites show low dielectric loss property.