SiC/SiC composites have emerged as essential thermal structure materials for development of hypersonic vehicles and high thrust-to-weight ratio aero-engines. Design and utilization of boron-containing ceramic precursors as impregnation agents for precursor infiltration and pyrolysis (PIP) to introduce self-healing components into matrix represent a key strategy for enhancing the antioxidant properties of SiC/SiC composites. Here, borane pyridine or borane triethylamine were utilized as boron sources and subsequently mixed with a solid polycarbosilane (PCS) xylene solution to prepare different boron-modified PCS solutions. These solutions were used as PIP impregnation agents to fabricate various boron-modified SiC/PyC (pyrolytic carbon)/SiC composites. The physicochemical properties of boron-modified PCS-derived ceramics, along with the physical and mechanical properties of SiC/PyC/SiC composites before and after matrix boron modification, were investigated. Results demonstrated that addition of appropriate amounts of borane pyridine and borane triethylamine as boron sources in solid PCS solutions effectively introduced boron as a heterogeneous element into the derived SiC ceramics. Compared to PCS, the boron-modified PCS solutions (BP-1 and BP-2) exhibited increased ceramic yields. The derived ceramics exhibited a semi-crystalline β-SiC structure, with boron element contents of 1.7% and 2.2% (in mass), respectively. In contrast to unmodified composite, the boron-modified SiC/SiC composites exhibited negligible changes in density, apparent porosity, and fracture toughness. However, the flexural modulus increased from 116 GPa to 132 GPa. Furthermore, the flexural strength of the modified composite using borane pyridine alone as boron source was 658 MPa, comparable to the unmodified composite's strength of 643 MPa, but with a reduced dispersion coefficient. All above data demonstrate that borane pyridine can be used as boron source for preparation of boron-modified SiC/SiC composites, providing valuable insights for developing high-performance SiC/SiC composite hot-end components.