The kinetics of the gas-phase reactions of chlorine atoms with bromomethane CH 3 Br and D-bromomethane CD 3 Br was studied experimentally. The relative rate method was applied using Cl+CH 4 as the reference reaction. The rate constants for H-abstraction from CH 3 Br (k H ) and D-abstraction from CD 3 Br (k D ) were measured in the temperature range of 298–527K and at a total pressure of 100Torr. The temperature dependencies of the rate constants are described by the expressions: k H =(1.43±0.22)×10 −11 ×exp(−1040±30/T) and k D =(1.36±0.31)×10 −11 ×exp(−1595±30/T)cm 3 molecule −1 s −1 . The kinetic isotope effect, described by the ratio k H /k D , was found to be (1.07±0.14)×exp(555±20/T).