Experimental results on the gas-phase extinction of diffusion flame for the pyrolyzed products of PMMA (polymethylmethacrylate) rods burning in laminar flows of O2/Nj mixtures are reported. Critical extinction conditions in terms of oxygen concentration, oxidizer mass flux and pressure are established. Kinetic parameters for the overall gas-phase oxidation process have been obtained from these results with the aid of recently-developed theoretical analyses for extinction of diffusion flames in the stagnation-point boundary layer of condensed fuels. Thus, on the basis of an overall reaction of order one with respect to oxygen and one with respect to PMMA-pyrolysis products, the experimental results provide values of 21 kcal/mole for the overall activation energy and of 3 × 1012cm5/ mole sec for the preexponential factor.