Two commercial acid dyes, Acid Orange 142 (E1) and Acid Violet 90 (E2), were applied to cotton and viscose fabrics treated with 3, 6 percent concentrations of chitosan and chitosan nanoparticles to impart absorption and antibacterial capabilities. The effect of chitosan and chitosan nanoparticles on the dyeing properties of cotton and viscose was investigated by measuring the colour strength expressed in K/S values of the treated substrates at various chitosan and dye concentrations. The results showed that fabrics treated with chitosan nanoparticles exhibited higher dye uptake and exhaustion than untreated fibres and fabrics treated with chitosan nanoparticles. Furthermore, the higher concentration of chitosan nanoparticles (6%) causes more tiredness than the lower dosage (3%). The antibacterial activity of fabrics treated with chitosan and chitosan nanoparticles is higher than that of untreated fabrics, indicating that chitosan nanoparticles treatment has the best antimicrobial properties. The rubbing, washing, and perspiration fastness properties of dyed cotton and viscose fabrics, as well as pre-treated fabric with chitosan nanoparticles and chitosan, were all tested, and the results revealed that all of the aforementioned dyes are excellent to good, and salt-free dyeing is both satisfactory. The colorimetric CIE L*a*b* C*h data of dyed cotton and viscose were also analyzed, and good results were found.