The thermal-neutron capture cross section of 147Sm has been measured by the mass spectrometric determination of the number of 148Sm atoms formed by neutron capture. Samples of high isotopic purity were irradiated in a well-thermalized neutron spectrum for which the time-integrated neutron flux and effective neutron temperature were monitored by the burnup in 149Sm and 157Gd. A thermal-neutron capture cross section value of 75 ± 11 b was obtained from a post-irradiation 148Sm/ 147Sm ratio of 0.00025 ± 8%, at an effective neutron temperature of 127 ± 13°C.