The 140Ba cumulative yield of irradiated uranium has been determined absolutely by a nondestructive method. Thin uranium foils are irradiated in the fast thermal zero-power reactor STARK. To avoid radiochemical separation, the 1596.5-keV gamma activity of 140La, the daughter nucleus of 140Ba, is measured with a high resolution (2.6 keV fwhm) Ge (Li) detector. From this 140La activity the absolute 140Ba yield is evaluated from the corresponding absolute fission rate and. the detector efficiency known for the 1596.5-keV photopeak. The uranium fission rate in the foil is normalized to the absolute fission rate measured with a calibrated parallel-plate chamber. Calibration of the gamma spectrometer is performed with activated thin La2O3 foils whose absolute activities are determined by 2π beta counting. The 140Ba cumulative yield data obtained are 6.29 ± 0.14% for 235 U thermal neutron fission and 6.10 ± 0.15(%) and 6.34 ± 0.41(%) for fast neutron fission of 235U and 238U, respectively. They are in good agreement (within ±1%) with the values reported to date.