Fiber-reinforced aerogel composites are extensively used in thermal insulation and energy-saving fields, while the inherently weak interface combination between fiber and aerogel undermines the effect of fiber reinforcement . To deal with this problem, mullite whiskers were in-situ synthesized on the surface of alumina silicate fiber through a facile and environmentally benign method. The nanoscale mullite whiskers growing on the fiber strengthen the interfacial bonding , thereby improving the mechanical properties of the composite. The alumina silicate fiber/mullite whisker/silica aerogel composites delivered ultrahigh compression stress and modulus of 6.45 MPa and 69.74 MPa at 50% strain, which is 6.14 times and 9.07 times higher than those of bare fiber reinforced silica aerogel . Meanwhile, the composite maintained a high retention rate of maximum stress of 97.8% after being compressed at 30% strain for 200 cycles. Moreover, the composite exhibits an ultralow thermal conductivity of 27.5 mW m −1 K −1 and a low density of 0.26 g cm −3 . The strong, resilient, lightweight composite with ultralow thermal conductivity is applicable for heat preservation and energy saving. • Mullite nanowhiskers were in-situ synthesized on alumina silicate fiber without F catalysts contaminating environment. • The stress (6.45 MPa) and modulus (69.74 MPa) at 50% strain increased dramatically due to interfacial enhancement. • The tough and resilient composite can be compressed at 30% strain for 200 cycles. • The composite also exhibited a low density (0.26 g cm −3 ) and a low thermal conductivity (27.5 mW m −1 K −1 ).