Boron-doped polycrystalline diamond films have been deposited over a molybdenum substrate by the microwave plasma CVD process using a methane and hydrogen gas mixture at a pressure of 35.7 Torr. Boron doping of diamond has been achieved in situ by using a solid boron source while growing diamond in the CVD process. The a.c. impedance of boron-doped diamond films in 0.5 M NaCl solution has been determined and compared with the results obtained with a molybdenum substrate. Capacitance, solution resistance, and polarization resistance (corrosion rate) have been determined using the experimental data plotted in Nyquist and Bode formats. D.C. polarization techniques such as linear and Tafel polarization have been used to evaluate the doped diamond coated molybdenum and molybdenum for corrosion resistance characteristics in terms of charge-transfer coefficients and corrosion rate. Cyclic voltammetry has been used to evaluate the molybdenum, platinum, and doped and undoped diamond coated molybdenum materials in 0.5 M NaCl solution, We have observed two time constants with a doped diamond electrode/solution interface. Solution resistance was found to be constant irrespective of the electrode in the same electrolyte solution.