The structural and luminescence properties of Zn1−xCdxSe/ZnSe multi-quantum well (MQW) structures with high molar fraction of cadmium (30–50%) and wide ZnSe barriers (50, 100 and 500nm) grown by molecular beam epitaxy (MBE) have been investigated by high-resolution X-ray diffraction (HRXRD) and photoluminescence (PL) methods. It is shown that the fluctuations of composition within the quantum well layer determine the full-width at half maximum (FWHM) of the QW photoluminescence peak. The unusual polarization characteristics of this photoluminescence have been observed. The emission peak in the edge geometry is strongly polarized perpendicularly to the QW plane. This effect is ascribed to the localization of the ground-state heavy-hole-like excitons in the regions with increased cadmium content.