In this study, swelling behavior of polyelectrolyte poly(hydroxamic acid) (PHA) hydrogels have been investigated in aqueous thiazin dye solutions. PHA hydrogels were prepared by free radical polymerizations of acrylamide with some cross-linkers such as N,N ' methylenebisacrylamide (NBisA) and ethylene glycol dimethacrylate (EGDMA); then they were used in experiments on swelling and diffusion of some water-soluble cationic dyes such as methylene blue (MB), thionin (T), and toluidin blue (TB). Swelling experiments were performed in water at 25 degrees C, gravimetrically. The equilibrium swelling percent (S%) values of PHA hydrogels were calculated as 238-2705%. Some swelling kinetic parameters such as initial swelling rate, swelling rate constant, and maximum (theoretical) swelling percent were found. Diffusional behavior of dye solutions was investigated. Dye diffusion into hydrogels was found to be non-Fickian in character. Diffusion exponent (n) is over 0.50. For sorption of thiazin cationic dyes, MB, T, and TB to PHA hydrogels were studied by batch sorption technique at 25 degrees C. PHA hydrogels in the dye solutions showed the dark coloration. In the experiments of the adsorption, S-type adsorption in the Giles classification system was found.