Potentiodynamic polarization and electrochemical impedance spectroscopy were employed to test carbonitrided CP-Ti, treated by a relatively new method called pulsed-plasma electrolytic carbonitriding. The results show excellent corrosion resistance for modified CP-Ti. The effect of frequency and duty cycle of pulsed current were investigated. It was found that pulse frequency and duty cycle affect the size and porosity of nanocrystalline carbonitrides and by controlling these effective parameters surface modification can render the CP-Ti material extremely corrosion resistant.