The present study immobilized nanoscale zero-valent iron (nZVI) on multi-walled carbon nanotubes (MWCNTs) to enhance the reactivity of nZVI and prevent its aggregation. This novel composite (nZVI/MWCNT) was characterized by scanning electron microscopy and X-ray diffraction. The results showed that nZVI particles dispersed on the surface of the MWCNTs. The composite was used to remove the diazo dye Direct Red 23 from aqueous solution. The effects of nZVI to MWCNT mass ratio, nanocomposite content, solution pH, initial dye concentration and temperature were studied. The optimum nZVI/MWCNT mass ratio was 1:3. Batch experiments suggest that degradation efficiency decreased as the initial dye concentration increased and increased as the nanocomposite content increased, decreasing the pH from 8 to 4. The reaction followed a pseudo-first-order model under the operational conditions investigated in this study.