The diffusion coefficient of a reactive dye in sodium alginate thickener and viscosity of print paste were measured and discussed with varing sodium alginate concentration, temperature, hydrolysation of dye, urea, alkali and dye concentration. The diffusion coefficient of dye was increased rapidly by temperature rasing and a little by hydrolysation of dye. And it was decreased to some extent by the increase of sodium alginate, urea, alkali, and dye concentration. The activation energy of diffusion in the thickenery was also calculated from the relation of temperature and diffusion coefficient: it indicated around 8.4 kcal/mole.