Hybrid gels were synthesized from modified silicon alkoxides (R-Si(OEt)(3), R = H, Me, Vi) and triisobutylborate (B(O-R')(3), R' = isoBu). The obtained gels were characterized by Fourier-transform infrared (FTIR), nuclear magnetic resonance (NMR), elemental analyses, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Boron atoms in the precursors were homogeneously dispersed in the siloxane network via Si-O-B bonds. The effect of the boron load on oxidation resistance of the gels, and the pyrolysis behavior of the borosiloxane gels with different substituents on silicon, were investigated using various techniques. The experimental results suggest that the addition of a proper fraction of boron alkoxide to the precursors can improve the oxidation stability of the gels, and decrease the weight loss of the samples to 6.9 wt % at 1000 degrees C under air. (c) 2005 Wiley Periodicals, Inc.