The kinetics for the gas-phase reaction of phenyl radicals with aliene has been measured by cavity ring-down spectrometry (CRDS), and the mechanism and initial product branching have been elucidated with the help of quantum-chemical calculations. The absolute rate constant measured by the CRDS technique can be expressed by the following Arrhenius equation: k allene (T = 301 - 421 K) = (4.07 ± 0.38) × 10 11 exp[-(1865 ± 85)/T] cm 3 mol -1 s -1. Theoretical calculations, employing high level G2M energetic and IRCMax(RCCSD(T)//B3LYP-DFT) molecular parameters, indicate that under our experimental conditions the most preferable reaction channel is the addition of phenyl radicals to the terminal carbon atoms in aliene. Predicted total rate constants agree with the experimental values within 40%. Calculated total and branching rate constants are provided for high-T kinetic modeling.