Mesoporous gamma alumina fibres of high surface area, stable up to 1000 °C, were synthesized by bioreplica technique using sisal fibres as templates. Alumina formation during pyrolysis and calcination of fibres infiltrated with aluminium chloride solution has been studied, paying special attention to the interaction between the precursor and sisal fibres, using several experimental techniques such as ATR-FTIR, coupled TG-FTIR and thermo-XRD analysis. The morphology and microstructure of the resulting alumina fibres were characterized using SEM and TEM. The crystallographic analysis of the alumina sample performed by electron and X-ray diffraction suggests that fibres are constituted by η and γ-Al2O3 crystallites, whose chemical structure was confirmed by ATR-FTIR and Al27-MAS-NMR. The specific surface area and porosity of ceramic fibres were determined by N2 and CO2 adsorption–desorption measurements. Resulting alumina fibres retain high specific surface areas of 200 and 150 m2/g even after calcination at 1000 °C for 15 h in dry air and for 4 h in wet air, respectively.