Rate constant for the reaction of OH with HFC-365mfc (CF3CH2CF2CH3) has been measured at a total pressure of 100 Torr, using the laser photolysis-laser induced fluorescence technique. The obtained kinetic data were used to derive the following Arrhenius expression over the temperature range 269--370 K: k=(1.68¿0.21)¿10-12 exp[-(1585¿80)/T> cm3 molecule-1 s-1. At 298 K, the measured rate coefficient was: k=(8.69¿0.74)¿10-15 cm3 molecule-1 s-1. This study is the first investigation to be reported on this reaction. Using our kinetic data, the tropospheric lifetime of CF3CH2CF2CH3 is estimated to be 7.8 years. ¿ American Geophysical Union 1995