In this paper, a dual-band quadrature coupler is proposed for arbitrary power divisions using the composite right/left-handed (CRLH) transmission lines. The presented prototype is based on two identical CRLH transmission lines of 50 ohm and a pair of lumped-element parallel tanks loaded to the CRLH host lines. The power division ratio at either frequency is determined by the electrical length of the 50-μ CRLH lines, which facilitates coupler realization of arbitrary power split, even for a large division ratio. By applying the CRLH lines, the dual operating frequencies as well as the corresponding power split ratios can be arbitrarily designed, which on the contrary is infeasible by microstrip lines. Two coupler prototypes were developed for power division ratios of 10/10 dB and 10/6 dB at 0.9/1.8 GHz. In particular, the first fabricated coupler occupies only 18% footprint of the 0.9-GHz microstrip branch-line coupler. Experimental results are in good agreement with simulation data.