[en] The ²³⁵U neutron fission cross section was measured relative to neutron-proton scattering from 5 to 800 keV neutron energy. The experiment was performed on the 200 m flight path at the NBS electron linac using a hydrogen gas proportional counter as a neutron flux monitor. This relative measurement was normalized by means of a second experiment on the 23 m flight path. This experiment, which used a 0.5 mm ⁶Li glass for a flux monitor, covered the energy region from 6 eV to 30 keV, and, normalized to an integrated cross section of 238.4 eV b in the 7.8 to 11.0 eV region, yields an average cross section of 2.48 +- 0.05 b for the 10 to 20 keV interval. The resultant cross section in the 200-800 keV interval is approximately 5 percent less than the ENDF/B-IV evaluation