For detoxification of Cr(VI)-contaminated water, a new process concept of using conductive polypyrrole/cellulose fiber composite (prepared by in situ polymerization of pyrrole in the presence of cellulose fibers) for water treatment was proposed and demonstrated. The effects of preparation conditions of the composite, as well as the water treatment conditions, on the detoxification efficiency were studied. Under the optimized conditions, the composite was highly effective in Cr(VI) detoxification. The desorption results and XPS analyses showed that the highly toxic Cr(VI) was reduced to less toxic Cr(III) and then adsorbed onto the composite. At least 3/4 of the Cr adsorbed to the composite was Cr(III). ATR-FTIR spectra and SEM images also proved that redox reaction occurred during the water treatment process. The integrated reductive/adsorptive Cr(VI) detoxification by polypyrrole-engineered cellulose fibers would provide new possibilities for the commercial application of conductive fibers.