The kinetics of gas reaction by multiphoton ionization method is reported. The detection of NO is made by the resonant multiphoton ionization of NO via the C2H state. The rate constant of NO reaction with O3 is obtained to be 1.1 X 10-14cm3 mol-1s-1 in a flow system, in good agreement with previous data. It should be considered that the photodissociation of NO2 will also contribute to the MPI signal at 365.45nm. Apparent dissociation rate of about 50% at this wavelength has been obtained.