Novel fibre-silica-Ag composites with biocidal activity were successfully produced by chemical modifying cotton (CO), wool (WO), silk (SE), polyamide (PA) and polyester (PES) fabrics and CO/PES and WO/PES fabric blends. A silica-Ag coating was prepared using a two-step procedure that included the creation of a silica matrix on the fibre surface via the application of an inorganic-organic hybrid sol-gel precursor [reactive binder (RB)] using a pad-dry-cure method, followed by the in situ synthesis of AgCl particles within the RB-treated fibres from solutions of 0.10 mM and 0.50 mM AgNO3 and NaCl. The presence of the coating on the fibres was verified by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The bulk concentration of Ag in the coated fibres was determined using inductively coupled plasma mass spectroscopy. The antimicrobial activity was determined for the bacteria Escherichia coli and Staphylococcus aureus and the fungus Aspergillus niger. The results show that the chemical and morphological structures of the fibres directly influenced their absorptivity and affinity for the Ag compound particles. As the amorphous molecular structure of the fibres and the amount of functional groups available as binding sites for Ag+ were increased, both the silver solution uptake and the concentration of the absorbed Ag compound particles increased. The chemical binding of Ag to the fibres significantly reduced the effectiveness of the antimicrobial activity of the Ag compound particles. Accordingly, an increase in the concentration of absorbed Ag was required to achieve a biocidal effect.