The increasing concerns on O3 pollution urgently demands high performance O3 sensors based on metal oxide semiconductors. Despite of noticeable progress, it’s still challenging to achieve highly sensitive and selective detection of trace O3 in ambient humid air with low power consumption. In this study, O3 sensors based on porous CuO nanomaterials synthesized via a simple solution combustion method have been proposed. By optimizing the fuel to oxidizer ratio, a high response (2.6 @ 10 ppb and 42 @ 50 ppb O3 under 70% RH), superior selectivity with the responses to diverse interfering gases in high concentration (10 ppm H2S, SO2, NO2, 50 ppm NH3, C2H6O, CH4O, C3H6O) less than 10 under 70% RH, outstanding repeatability and long-term stability at working temperature of 70 °C were achieved by the present CuO based O3 sensor. A smart O3 monitoring system based on CuO sensor has been developed, which could facilely monitor the leakage of O3 in ambient humid air, indicating great potential for practical application in environmental O3 detection.