Abstract: An experimental study of the chemiluminescent reaction of Sn with N_2O and O_2 is first performed in a supersonic flow apparatus by using the electric-arc plasma technique to generate atomic Sn vapor. The temperature and pressure in the reacton zone are 900 K and 1-10 torr, respectively. The emission spectra of SnO (a~3Σ~+-X~1Σ~+) are recorded using an optical multichannel analyzer (OMA) at different reaction pressures and the dependence of the relative vibrational population of the product SnO(a~3Σ~+), on the pressure has been presented. The vibraitional relaxation rates of the SnO (a~3Σ~+) by Ar and Ar+N_2 had been calculated as ～10~4 torr~(-1) s~(-1) by the leastsquare fit of the experimental data. The emissions from the electronically excited states, b~3Π and a~3Σ~+, in the reaction of Sn+O_2 can be explained in terms of the reactions of Sn_2+O_2 and Sn_2+O. An unusually high population of a~3Σ~+v′=1 in the reaction of Sn+O_2 is also found. The results are compared with those obtained in high-temperature-fast-flow reactor (HTFFR) and the reaction mechanism is discussed.