Isomer yield ratio measurements in fission are important in understand
ing the fission process. With the development of new instrumental tech
niques, a large number of yield data are now available. The experiment
al data on isomer yield ratios in the thermal neutron induced fission
of U-235 compared with those calculated from the simple statistical mo
del by MADLAND and ENGLAND. The method of calculation has been extende
d to the isotopes having more than one isomeric state. The results may
be explained according to the multi-exit-channel model of fission.