P-type CuO nanorods with the breadth of 15–20 nm and the length of 60–80 nm, have been synthesized using a microwave-assisted hydrothermal (MH) method. The band gap of CuO nanorods was calculated to be 2.75 eV based on the UV–vis absorption spectrum of the product. The gas sensing property of the CuO nanorods to several organic vapors was tested in temperatures ranging from 160 °C to 300 °C. The response of the CuO sensor to ethanol (1000 ppm) was 9.8 at the working temperature of 210 °C. The response time and the recovery time were within the range of 13–42 s and 17–51 s, respectively. Further measurements exhibited stronger response to ethanol than to other target gases. The enhanced gas sensing performance of the sensor to ethanol may be attributed to the small size of the CuO particles.