A composite fiber of polyacrylonitrile (PAN) and chitosan was obtained by spinning the mixture of PAN/chitosan with a certain amount of diluted acetic acid as a plasticizer. Water plasticizes the PAN and acetic acid plasticizes the chitosan. The fiber showed a porous and fibrillar structure, which could be converted easily into pulplike short fiber by pulping. PAN/chitosan pulp showed a much higher amount of uptake for acid dye than that of either powdery chitosan or activated carbon. It is considered that this better sorption capacity of the composite fiber results from the relatively large surface area attributed to its pulplike shape. The adsorption behavior of the composite fiber was considerably affected by temperature and pH because the adsorption is exothermic and proceeds by an acid-base reaction.