The absolute fission yields of 22 nuclides formed in the thermal neutron fission of U233 have been measured radiochemically. Disintegration rates were measured by 4π β-proportional counting techniques. The identity of each nuclide was established by chemical separations and decay characteristics as determined by 4π β-counting and γ-ray scintillation spectrometry. The reaction Co59(n, γ)Co60 was used as a neutron flux monitor. Yields were calculated on the basis of [Formula: see text]