The reaction kinetics of C2H3 + O-2 has been studied at room temperature, where, CH2CHO produced in this reaction is monitored quantitatively by using a laser induced fluorescence technique. The reaction rate constant is obtained as (8.5 +/- 1.0) x 10 (12)cm(3) molecule (1)s(1) with almost no pressure dependence for the range of 10-100 Torr (He): the present result is consistent with the previous experimental studies. Also by using two different precursors as a source of C2H3, the branching fraction of producing CH2CHO + O channel is determined as phi(CH2CHO) = 0.14-0.21, i. e., O-O bond scission in the reaction intermediate, vinylperoxy radical, is confirmed, exhibiting clear contrast to alkylperoxy radicals. (C) 2009 Elsevier B. V. All rights reserved.