An arbitrary impedance-transforming dual-band out-of-phase power divider using double-sided parallel-strip line (DSPSL) with inserted conductor plane is proposed. This out-of-phase power divider is mainly composed of two two-section dual-band impedance transformers, a conductor plane transforming DSPSL into microstrip lines, and four resistors. Odd and even-mode analyses show that the proposed power divider is able to operate at two frequencies of and with a wide frequency ratio range at . The proposed power divider has been demonstrated and verified. The experimental results show that the proposed out-of-phase power divider can realize the impedance transformation from to with good return losses, fine isolation, low insertion losses and high stability of 180 phase difference.