A novel time-resolved microwave sensor was developed to probing information of reaction kinetics, which is of fundamental importance for the understanding of the catalytic processes and the synthesis of catalyst. The processes of the decomposition of acetaldehyde on different catalysts (Cd/MCM-41, Ce/MCM-41, Co/MCM-41 and Ni/MCM-41) had been detected by the sensor, respectively. The results showed that it was possible to use time-resolved microwave sensor for probing the information of reaction kinetics.