In this paper, the influence of plasma nitriding at temperature 720 degreesC for 20 h on the surface microstructure and interface microstructure of electroplated chromium coating was investigated. In these conditions, interdiffusion, mixing and reaction phenomena of elements originating from the substrate and coating material are more likely to occur. thus increasing the bonding strength between the coating and carbon steel substrate. The change of the structures from the substrate side to the coating surface, and the effect of the substrate steel on the interface structure were studied by cross-sectional transmission electron microscope observation (XTEM). The nitride layer formed on the surface was analyzed by X-ray diffraction method (XRD). After treatment at above conditions a 6-7 mum thick nitride compound layer was formed in surface region and the same thick carbide compound layer was also formed in the interface region between electroplated chromium coating and mild carbon steel substrate. (C) 2003 Elsevier Science B.V. All rights reserved.