New fibre-reinforced composites of aluminosilicate inorganic polymer (geopolymer) with natural protein-based fibres (carpet and Merino wool) were developed, and their mechanical properties determined. The surfaces of some of the wool fibres used in this study were chemically modified to improve their alkali resistance and reinforcing properties. The flexural strengths and failure characteristics of the composites, determined on bar-shaped samples by a three-point test method, show an approximately 40 % improvement over the unreinforced matrix and graceful failure, unlike the unreinforced matrix that displays ceramic-like brittle fracture. Interaction between the sulphide linkages of the wool and the aluminosilicate matrix produces a blue-green colour in the wool, shown by UV-visible and IR spectroscopy to be related to the formation of the sulpho-aluminosilicate compound sodalite. The thermal behaviour of these composites was studied by thermogravimetric analysis, and scanning electron microscopy was used to study the fibre-matrix interface.