As an attempt to combine the dyeing and functional finishing steps into one process, two novel anti-bacterial monoazo acid dyes based on N-ester-1,8-naphthalimide were synthesised. To do this, 4-amino-N-ethyl glycinate-1,8-naphthalimide was prepared, diazotised and then coupled to thiosalicylic acid or salicylic acid to produce anti-bacterial dyes. The synthesised dyes were purified and then fully characterised using Fourier Transform–infrared spectrometry, proton nuclear magnetic resonance spectroscopy and melting point analysis. Dispersion of the dyes was prepared in water and applied to nylon 6 fabrics. The novel dyes offered good build-up properties on the substrate. The anti-bacterial efficacy of the synthesised dyes was assessed, with the dyes showing activity against both Gram-positive and Gram-negative bacteria.