CuO hollow microspheres were synthesized via a facile hydrothermal process. Copper nitrate trihydrate (Cu(NO3)(2)center dot 3H(2)O) was used as copper source and cetyltrimethylammonium bromide (CTAB) was used as soft template. The morphology and crystal structure of products were systematically investigated by XRD, FESEM, TEM, FT-IR and BET. CuO hollow microspheres were identified as monoclinic structure. The hollow microspheres were assembled by a number of nanobars which were composed of smaller nanograins. The formaldehyde gas sensing properties of CuO products with different morphologies were investigated. The results indicated that the sensor based on CuO hollow microspheres exhibited high gas response, fast reversible and response, good selectivity and stability to formaldehyde gas. This is attributed to hollow structures with the largest specific surface area and an effective gas diffusion path in favor of mass transportation and gas diffusion. (C) 2017 Elsevier Ltd. All rights reserved.