Neutron transmission measurements have been made on two high-purity samples of 243Am having inverse thicknesses of 1288.2 and 279.3 b/atom, respectively. Data were collected from 0.5 to 1000 eV using the Oak Ridge Electron Linear Accelerator. High resolution data were taken using 10- and 30-nsec bursts of 140-MeV electrons, 10-nsec channel widths, and a flight path of 18.576 m. An average value of Ty of 39 ± 1 meV was determined from shape analysis of 24 resonances below 18 eV. Single-level Breit-Wigner resonance parameters were obtained from area analysis up to 250 eV. The average level spacing between resonances was found to be 0.68 ± 0.06 eV. An s-wave neutron strength function of (0.96 ± 0.10) × 10≈4 was determined from the resonance parameters, The resonance-absorption integral for neutrons with energies above 0.625 eV was determined to be 1810 ± 70 b from the resonance parameters.