In this investigation, the electroless copper method with various cupric sulfate concentrations (0.24, 0.36, 0.48, 0.60M) without sensitizing and activating is used to deposit electroless copper compounds (CuS) on the swelling pretreatment polyacrylonitrile(SPAN) surface for electromagnetic interference (EMI) shielding materials. The acetic acid can swell polyacrylonitrile (PAN) effectively which donot destroy the hexagonal structure of polyacrylonitrile, only looses the molecule chain of polyacrylonitrile then the hexagonal CuS crystal deposits on the SPAN easily, and increases the EMI shielding effectiveness (SE) of CuS-SPAN composites. However, the nearly amorphous of CuS deposits on the surface of without swelling pretreatment PAN(CuS-PAN). The EMI SE of CuS-SPAN composites are better than those of CuS-PAN, 10-15 dB larger from CuS-PAN. In the study, the best EMI SE of CuS-SPAN and CuS-PAN composites are about 30-35 dB and 18-20 dB respectively, as the cupric ion concentration is 0.48M. From the high resolution transmission electron micrographs(HR-TEM) analysis, there are two structures, face-centered cubic(FCC) Cu2-xS crystal in the inner layer of CuS-SPAN composite and hexagonal CuS crystal on the outer layer of CuS-SPAN composite, in the SPAN as the cupric ion concentration is 0.48M. The particle size distribution of Cu2-xS in the inner layer of CuS-SPAN is from 6 to 30 nm. However, the major particle size distribution of Cu2-xS in the, inner layer of CuS-SPAN is from 15 to 20 nm. (c) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 109: 3679-3688,2008.