The reaction of CF2(($) over tilde X(1)A(1)) with O-3 has been investigated in an isothermal flow reactor at temperatures between 300 and 600 K and pressures in the range 4 less than or equal to P/mbar less than or equal to 5. CF2(($) over tilde X) was produced by a microwave discharge of CF2Br2/He mixtures and detected by laser-induced fluorescence (LIF). [CF2(($) over tilde X)](t) profiles were measured under pseudo-first-order conditions ([CF2)(($) over tilde X)](0) much less than [O-3](0)). The rate constant of the reaction CF2(($) over tilde X + O-3(($) over tilde X) --> products (1) was determined, k(1)(T) = 1.9 x 10(12) exp(-(25 +/- 8) kJ mol(-1)/RT) cm(3) mol(-1) s(-1) (300 less than or equal to T/K less than or equal to 600). An estimation of the rate constant for the reaction CF2(($) over tilde X + O-2(X) --> products (2) can be given as k(2)(800 K) less than or equal to 5 x 10(6) cm(3) mol(-1) s(-1).