Ni-Cu-P/carbon nanotubes (CNTs) quaternary composite coatings were successfully obtained on low carbon steel matrix by electroless plating. The effects of CNTs concentration in the bath on the microstructure of the composite coatings, CNTs content in the composite coatings and the hardness of composite coatings before and after heat treatment at 400 T have been studied. In addition, the corrosion resistance of Ni-Cu-P/CNTs composite coatings was evaluated by anodic polarization curves in 3.5 wt.% NaCl solution at room temperature. It was noted that the CNTs concentration remarkably influenced the surface morphology of the coatings, With increasing CNTs concentration. both the CNTs content in the composite coatings and the hardness of composite coatings increased at first and then decreased. And the composite coatings after heat treatment provided higher hardness than the as-deposited coatings. The corrosion resistance of Ni-Cu-P/CNTs composite coatings is excellent compared with that of Ni-Cu-P coatings. (C) 2008 Elsevier Ltd. All rights reserved.