In this work, nanostructured copper oxide of varied morphologies and high surface area were prepared by calcination of copper oxalate precursors, and were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis and differential thermal analysis, and nitrogen adsorption-desorption measurements. The sphere-like CuO (specific surface area: 73 m(2) g(-1)) functionalized QCM resonators were fabricated and explored for HCN sensing. The sensitivity (10 s HCN exposure) of sphere-like CuO functionalized QCM resonators reached as high as 6.53 Hz μg(-1). The reproducibility and stability of sphere-like CuO functionalized QCM resonators was excellent, and the selectivity was very high with a converse response to examined common chemicals. The high surface area CuO functionalized QCM sensors may be applicable for HCN gas sensing.