An apparatus for estimating a steering angle of MDPS including: a motor of an MDPS, corresponding to rotation of a steering wheel; an amplifier configured to amplify a specific level of counter electromotive force to a preset level and output the amplified voltage, the specific level of counter electromotive force being generated by the motor when the steering wheel is manually operated; a switch configured to be turned on by the amplified voltage outputted from the amplifier; a power supply configured to be turned on by the switch and supply power to the MDPS; and a control unit of the MDPS configured to be driven by the supplied power and estimate a steering angle of the steering wheel, which is manually operated.