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Abstract: In this paper, a low-profile dual-broadband dual-circularly-polarized (dual-CP) reflectarray (RA) is proposed and demonstrated, supporting independent beamforming for right-/left-handed CP waves at both K- and Ka-bands. Such functionality is achieved by incorporating multi-layered phase shifting elements individually operating in the K- and Ka-bands, which are then interleaved in a shared aperture, resulting in a cell thickness of only about 0.1λ_L. By rotating the designed K- and Ka-band elements around their own geometrical centers, the dual-CP waves in each band can be modulated separately. For reducing the overall profile, planar K-/Ka-band dual-CP feeds with a broad bandwidth are designed based on the magnetoelectric dipoles and multi-branch hybrid couplers. The planar feeds achieve bandwidths of about 32% and 26% at K- and Ka-bands with reflection magnitudes below -13 dB, an axial ratio smaller than 2 dB, and a gain variation of less than 1 dB. A proof-of-concept dual-band dual-CP RA integrated with the planar feeds is fabricated and characterized, which is capable of generating asymmetrically distributed dual-band dual-CP beams. The measured peak gain values of the beams are around 24.3 and 27.3 dBic, with joint gain variation < 1 dB and axial ratio < 2 dB bandwidths wider than 20.6% and 14.6% at the lower-band and higher-band, respectively. The demonstrated dual-broadband dual-CP RA with four degrees of freedom of beamforming could be a promising candidate for space and satellite communications.