Hybrid SnO2/SWNTs thin layer were deposited by using sol-gel process. Such sensitive layers showed very high performances for O3 flow detection at ambient temperature. Limit sensitivity, lower than 21,5 ppb of O3 in air has been reached by using these hybrid layers. Compared to usefull metal oxide sensors, the main advantage of the use of such hybrid layers, is that these devices enable the detection of O3 traces at room temperature. The influence of sensor's working temperature is discussed and finally a reactional mechanism for the detection of O3 is proposed.