The possibility of using sawdust as an adsorbent in a fixed-bed adsorber in decolorizing wastewater as well as batchwise was studied. The Freundlich isotherm was obtained for the adsorption of a basic dyestuff (Maxillon Blue) on wood. The factors studied under isothermal adsorption conditions include feed input velocity, wood particle size, and bed height. The controlling step of adsorption at relatively high velocities is the internal diffusion within the pores rather than the external diffusion. The results showed that the best operating conditions were obtained at an intermediate feed velocity of 0.12 cm/s, a particle diameter of 0.018 cm, and a bed height of 10 cm.