Abstract: Gross fission product gamma-ray spectra are obtained using a large volume Ge(Li) detector,and then,the total energy peaks corresponding to 99Mo 739 keV and 95Zr 756 keV gamma-rays are analysed. The R value, which is the ratio of 99Mo relative cumulative yields for fast and thermal fission of 235U,are determined.Absolute cumulative yield of 99Mo is obtained based on the normalization of the R Value to the reference values of FPYs concerned.Up to now,the published data can be divided into two groups:the one,~6.40,and the other,~6.10.Our result,6.12(1±2.8%),agrees well with the latter.