Cobalt-Phosphorous (Co-P) alloy thin films were prepared by electrodeposition technique from an aqueous electrolytic bath at various sodium chloride (NaCl) concentrations. The effect of sodium chloride concentration on electrochemical, structural, morphological, compositional and magnetic properties of the films was investigated by cyclic voltammetry, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and vibrating sample magnetometer techniques, respectively. The mechanism of formation of Co-P alloy thin films was studied using cyclic voltammetry. The compositional analysis shows that the content of phosphorous (P) increases and the content of cobalt (Co) decreases by adding NaCl. X-ray diffraction studies revealed amorphous nature for. lms obtained at high concentration of NaCl and hexagonal closed packed (hcp) structure for. lms obtained at low NaCl concentration. Magnetic properties illustrate that high value of coercivity, saturation magnetization, remanence, and saturating field were obtained at high concentration of NaCl. (C) 2009 Elsevier B.V. All rights reserved.