With the proliferation of the use of wireless communication technologies, lightweight, easily fabricated electromagnetic wave (EMW) absorbers are in great demand for commercial and stealth applicationS In this paper, well-defined Cu2O microcubes were successfully converted into S-doped Cu2 − xSe micro-cubic boxes at room temperature by a template-directed in situ selenization/sulfidation reactioN the Cu2 − xSe boxes were obtained under the combined effect of Kirkendall effect and Ostwald ripening, and the composite products with paraffins exhibited good EMW low-frequency absorption properties at 40 wt%, with RL(min) exceeding − 20 dB from 2.6 mm-5.0 mM In addition, the sulfidation process optimized the morphology, composition, interface, defects, and conductivity, which further enhanced the EMW absorption performance of the materiaL The optimized RL(min) of S-doped Cu2 − xSe reaches − 44.5 dB at 1.9 mm with an EAB of 4.3 GHZ