Display omitted •Developed a high-sensitive CuO/rGO heterostructures sensor for NO2 gas detection at RT (30 °C).•The CuO/rGO heterostructures (CR10) sensor showed an incredibly high sensitivity of 1004 % against 5 ppm NO2 gas.•The CuO/rGO heterostructures (CR10) sensor exhibited extremely rapid response rate of 10 s at RT.•The developed NO2 sensor displays high selectivity, long-term stability (30 days), good linearity, and impressive repeatability. The process of combusting non-renewable energy sources results in the emission of a variety of harmful gases into the environment. As a result, there is a continuing need for a high-sensitivity gas sensor capable of promptly identifying these gases at room temperature (RT). Herein, we developed a high-sensitive CuO/rGO heterostructures sensor for NO2 gas detection at RT (30 °C) with enhanced sensitivity and short response rate. Interestingly, the developed CuO/rGO (CR10) sample illustrated an incredibly high sensitivity of 1004% against 5 ppm NO2 gas with an extremely rapid response rate of 9 s at RT. The developed CR10 sensor exhibits a 5.17 times ameliorated sensing response against 5 ppm of NO2 gas in contrast to the pristine CuO (CR0) sensor. The developed NO2 sensor also exhibits high selectivity, long-term stability (30 days), good linearity, and impressive repeatability. The synergistic interaction between CuO and reduced graphene oxide (rGO) are primary reason for the enrichment of the sensing performance. In particular, a thin layer of rGO arranged over CuO porous nanosheets and the enormous surface area of CuO/rGO could serve as additional available adsorption centres for NO2 gas and increase the speed of redox reaction on the CuO/rGO sensor surface, resulting in an extremely high sensing response. Furthermore, the rGO thin layer exhibits exceptional carrier transfer capabilities that can be utilized as ultra-responsive conductive channels, thereby enhancing the sensing response significantly. Besides, a significant amount of chemisorbed oxygen species are also relatively favourable for the sensing performance. This study opens up a novel avenue to develop a high-performance NO2 sensors at RT.