Nickel-alumina nano-composite coatings were obtained from nickel sulphamate solution containing nano-alumina particles by direct current (DC) plating. Nano-alumina particles were dispersed in the solution with the aid of different concentrations (50-300 mg l(-1)) of the anionic surfactant sodium dodecyl sulfate (SDS) by ultrasonic method. The microhardness variation of the coatings in different concentrations of SOS was investigated. Furthermore, the corrosion behavior of composite coatings was studied by polarization measurements in 3.5% w/v NaCl solution. The results revealed that increasing the surfactant concentration, up to an optimum value (125 mg l(-1)), led to more uniform distribution of nano-particles in the coatings, improved corrosion potential (E-corr) to the most positive value (-0209 V) and corrosion current density (i(corr)) to the lowest value (1.141 x -7 A cm(-2)), and enhanced the microhardness of composite coatings to 492 HV. However, beyond this optimum level, these properties were attenuated. (C) 2012 Elsevier B.V. All rights reserved.