This article reports the effect of the mixing process on the electromagnetic interference (EMI) shielding effectiveness of nickel/acrylonitrile-butadiene-styrene (ABS) composites. Nickel in either powder or filament form was used as the filler material. It was mixed with ABS by two mixing processes: one was the Brabender-mixing method, in which nickel was; mixed in the polymer melt by a strong shear at high temperatures, and the other was a simple dry mixing method performed in a centrifugal ball mill. Our results showed that the dry-mixing method could produce EMI shielding effectiveness of 36 dB at the 3 vol % nickel filaments level. In contrast, we need 20 vol % nickel powder to exhibit some shielding effectiveness for the Brabender method. After the nondestructive X-ray examination and four-point probe resistivity measurements, we concluded that better EMI shielding effectiveness could be achieved when the mixing method provided a state of uniformity on the macroscale, but not on the microscale. © 2005 Wiley Periodicals, Inc.