In order to improve flame retardance and thermal stability of wool fabric, a series of boron doped silica sols were prepared from a tetraethyl silicate inorganic precursor and applied to wool fabric as a flame retardant finish through the sol–gel process. Boric acid, zinc borate and ammonium borate were used as flame retardant additives. The effect of the boron containing flame retardant doped sol coatings on flammability, combustion behavior and thermal property of treated wool fabric was investigated via limited oxygen index (LOI) test, vertical burning test, thermogravimetric (TG) analysis, micro-calorimeter combustion (MCC) and smoke density test. It was found that the coatings on wool fabric acted as a heat insulation barrier, increasing the carbon residue and slowing down the spread of flame when burning, thus improving the flame retardance and thermal stability of the treated fabric. Meanwhile, the smoke density result indicated that the NH4HB4O7 doped silica sol treated fabric had good smoke suppression property. Furthermore, the result of mechanical properties showed that there was no damage on tensile strength and air permeation of treated wool fabric.