The secondary electron yield from fission fragments has been measured directly using an ultrahigh‐vacuum diode containing uranium which was operated in a nuclear reactor. The current measured in this diode consisted of contributions from the positively charged fission fragments, secondary electron emission induced by fission fragments, and photoelectrons generated by gamma radiation. The secondary electron yield &Dgr; was determined from the secondary electron current and the computed fission fragment emission rate. For a thick (>one range) uranium‐nickel (5.7 wt. % nickel) alloy the value of &Dgr; is 207±10.