We successfully grew cubic InGaN epilayers having the InN molar fraction up to 20% on 3C-SiC (0 0 1) substrates by radio frequency Nz plasma molecular beam epitaxy. Cubic InGaN epilayers of 200 nm thickness on cubic GaN were found to be strained by high resolution X-ray diffraction (XRD) reciprocal space measurement. On the other hand, 450 nm thick cubic InGaN epilayers on cubic GaN were fully relaxed. The photoluminescence (PL) emission from the cubic InGaN epilayers was clearly observed at room temperature. The energy of the PL emission was decreased nonlinearly with the increase of InN molar fraction, and that of a In0.20Ga0.80N epilayer was as low as 2.1 eV. We also attempted to fabricate cubic InGaN/GaN multiple quantum well structures. Several satellite peaks of the superstructure were observed by XRD, which indicates the excellent quality of superstructure and hetero-interface.