Unbleached flax fibres were treated with laccase from Pycnoporus cinnabarinus and low molecular weight phenols (syringaldehyde –SA, acetosyringone –AS- and p-coumaric acid –PCA-) to biomodify lignocellulosic fibres in order to confer them antibacterial properties. After the enzymatic treatment, PCA, SA and AS produced an increase in kappa number (lignin estimation), which is due to a partial covalent binding of the phenoxy radicals on pulp. To take advantage of the tendency of these natural phenols to couple to fibres, a standard method to determine bacterial growing inhibition was carried out. Antimicrobial properties of the pulps were tested on S. aureus, P. aeruginosa and K. pneumonia. Treated pulps produced a greater reduction in viable organisms than the laccase control after the same contact time, in some cases nearly total organism elimination was seen. Optical properties of treated papers were also measured in order to evaluate the possible coloration obtained. These results suggest that these low molecular weight phenols are covalently bounded to the flax fibres by the laccase and can act as antimicrobial agents.