Boost converter is widely used in DC power supply system. Its input voltage is often provided by AC power grid through an uncontrolled rectifier bridge. Due to that, there is obvious double-line frequency ripple especially in DC input voltage and inductor current. To solve this problem, a PI regulator with DC input voltage prediction is proposed in this letter. The reference duty cycle is calculated by a PI regulator, and then it is modified by the prediction. To predict well, the quadratic interpolation method with error correction is adopted. The effectiveness of the proposed method on double-line frequency ripple suppression is verified by experimental results.