Ni-P-ultrafine diamond (UFD) and Ni-P-carbon nanotubes (CNTs) composite coatings were deposited by electroplating at 76degreesC. The relation between the content of the incorporation and the amount of the UFD and CNTs in the electroplating solution was investigated. The corrosion behavior of the composite coatings was evaluated by polarization curves and electrochemical impedance spectroscopy in 0.1 M NaCl and 0.5 M H2SO4 solutions. It was found that increasing the UFD content in the coatings displays better corrosion performance, while a contrary result for the CNTs incorporated alloys was found due to the special structural state. The results show the incorporation of UFD and CNTs in Ni-P coatings is advantageous for forming better passive films. (C) 2004 Kluwer Academic Publishers