Polyacrylonitrile (PAN) hollow fibers were pretreated with ammonium dibasic phosphate aqueous solution, then further oxidized in air, carbonized in nitrogen, and activated with carbon dioxide. The effects of pretreatment time of PAN hollow fibers in ammonium dibasic phosphate aqueous solution on the microstructure, specific surface, pore-size distribution, and adsorption properties of PAN-based activated carbon hollow fibers (PAN-ACHF) were studied in this work. After the activation process, the Brunaner-Emmett-Teller (BET) surface area of the PAN-ACHF and surface area of mesopores in the PAN-ACHF increases and reaches 513 m(2) g(-1) and 66 m(2) g(-1) respectively, when the dipping time of PAN hollow fibers in ammonium dibasic phosphate aqueous solution is 30 min. The adsorptions to creatinine and VB12 of PAN-ACHF are much high, reach 95% and 86% respectively, when dipping time is 30 min. The dominant pore sizes of mesopores in PAN-ACHF range from 2 nm to 5 nm. (c) 2006 Wiley Periodicals, Inc.