Activated carbon fibers and modified alginate were prepared by using a cheap precursor material. The adsorption behavior of these materials was studied toward basic dyes. It was found that the most effective factor in the adsorption process onto ACF is the high surface area followed by a little assist of the carboxylic groups on the surface. On the contrary, only the carboxylic groups created on the modified alginate ( MA) will govern the adsorption behavior of MA. The equilibrium time for ACF in the adsorption of basic dyes was found to be 37 min, whereas in MA it was 70 min. The difference in the adsorption rate between ACF and MA was attributed to the difference in their structure features. Langmuir and Freundlich isotherm models were tested in the study to compare their applicability with the adsorption systems used. The result revealed that the adsorption of basics dyes onto ACF and MA fit very well with both Langmuir and Freundlich isotherms. The adsorption of basic dyes onto ACF follows the micropore-filling mechanism, whereas in MA, the adsorption is done via a physicochemical interaction between the dyes molecules and the carboxylic groups onto MA.