For better understanding of the molecular reactions in the nonthermal plasma reactor excited by the nanosecond pulse in atmospheric pressure, an atomic oxygen measuring system for the needle to plate discharge plasma was constructed by using the two-photon absorption laser-induced fluorescence (TALIF) principle of 226 nm two photon irradiation. The lifetime of the atomic oxygen is about a few tens of microseconds and immediately decreases. (c) 2005 Elsevier B.V. All rights reserved.