Highly pure cellulose fibers were coated with polypyrrole (PPy) and subsequently used for preparation of composites, which reached a certain level of electrical conductivity. The cellulose fibers surface was entirely covered when 20 wt % of pyrrole was used for the modification, as confirmed by scanning electron microscopy (SEM). The cellulose fibers covered with PPy were kneaded with thermoplastic matrices: linear low-density polyethylene (LL-DPE), high-density polyethylene (HDPE), and polycaprolactone (PCL). The highest electrical conductivity achieved was for composites based on the PCL matrix. PCL filled with 50 wt % of conducting cellulose fibers reached an electrical conductivity of 6.5 X 10(-4) S cm(-1). This electrical conductivity falls within the range required for antistatic materials. The mechanical properties of HDPE, LLDPE, and PCL matrices loaded with both treated and untreated cellulose fibers were also investigated. (c) 2006 Wiley Periodicals, Inc.