Abstract: In the present work fission yield method is developed to calibrate the fission fragment registration efficiency factor of solid state track detector immersed in uranium solution. After measuring the activity of some fission product nuclides and the track density on the track detector, the efficiency factor,Kwe, can be evaluated. It is based on the accuracy of thermal fission yield data of 235U. The fission product nuclides to be measured are 91Sr, 92Sr, "Mo, 132Te, 139Ba and 140Ba. The value of Kwet for polycarbonate is measured to be (8.52+±0.05)× 10-4cm which is in very good agreement with the value calibrated with 252Cf solution.