THE EFFECT of some swelling agents; Viz. alkali metal hydroxides, alkaline earth metal salt and heavy metal salt, on the dyeability of lyocell and modal fabrics with reactive and direct dyes was monitored. The dyeing characteristics; namely colour strength, dyeing isotherm, diffusion coefficient, dyeing rate constant and half dyeing time of the dyed fabrics were assessed. The colour strength of the dyed samples increased in the order ZnCl 2 > MgCl2> NaOH > KOH > untreated. The fastness properties of the dyed fabrics were investigated. X-ray diffraction patterns of both untreated as well as treated fabrics were used to assign the change in the fine structure of the swollen lyocell and modal fibres relative to their respective untreated ones. The water retention capacity of lyocell and modal fabrics was calculated to deduce the degree of crystallinty of treated as well as untreated lyocell and modal fabrics.