Absolute rate coefficients for the reaction of C2H with O-2 are measured at 90 K and 120 K by using a pulsed Laval nozzle apparatus with laser ionization, time-of-flight mass spectrometry (TOF-MS). The C2H radicals are generated by laser photolysis of C2H2 at 193 nm, and the products of the reaction with O-2 and C2H2, HCCO and C4H2, respectively, are directly detected by laser ionization at 118 nm. Rate coefficients of (9.0+/-2.0) x 10(-11) and (5.0 +/- 1.5) x 10(-11) cm(3) molecule(-1) s(-1) are obtained at 90 K and 120 K for the C2H + O-2 reaction, respectively, by detecting the rise of the product HCCO.