The thermal-neutron capture cross section and capture resonance integral for 243Cm have been measured in cobalt-monitored reactor irradiations of nearly isotopically pure 243Cm (99.94%) using cadmium filter techniques. The thermal-neutron absorption (capture plus fission) cross section and corresponding resonance integral for 243Cm have also been measured in a separate experiment relative to 248Cm. Values of σ2200(n, γ) = 130.7 ± 9.6, σ2200(n, f) = 609.6 ± 25.9, I(n, γ) = 214.7 ± 20.3, and I(n, f) = 1575 ± 136 b are reported.