The quick and accurate detection of acetone concentration in exhaled gas is particularly important to the diagnosis of diabetics. In this work, a flower-like CuO/ $\alpha $ -Fe2O3 heterojunction sensor derived from metal-organic framework was prepared by hydrothermal synthesis. The MOF-CuO/ $\alpha $ -Fe2O3 sensor has ultrahigh sensitivity and responds up to 75% toward 500-ppb acetone gas at 180° with a response/recovery time of 5/6 s. This is attributed to the large specific surface area of the formed MOF-CuO material, which provides more adsorption sites. At the same time, the heterojunction formed by CuO and $\alpha $ -Fe2O3 can also improve the surface carriers. In addition, by comparing the exhaled air of simulated diabetic patients with that of healthy individuals, it is proved that the sensor has a good prospect for the auxiliary diagnosis of diabetes.