The irradiation‐temperature dependence of the uniaxial anisotropy energyKuhas been examined for a series of well‐stabilized large‐grain([inverted lazy s]0.2 &mgr;)iron‐nickel alloy thin films having compositions between 44% Ni and 90% Ni. The uniaxial anisotropy was developed in these films by irradiating at temperatures of 125, 225, 275, 300, 325, and 400 °C, in the presence of a 180‐Oe magnetic field applied parallel to the film's easy direction of magnetization. Room‐temperature measurements ofKufollowing the irradiations indicate the development of three types of order: (i) iron‐iron pair short‐range directional order which is present for all compositions, (ii) NiFe long‐range order for films with compositions between 44% Ni and 70% Ni which were irradiated below 400 °C, and (iii) Ni3Fe long‐range order for film compositions around 75% Ni. The uniaxial anisotropy energy induced in films irradiated at 400 °C proved to be almost entirely the result of iron‐iron pair ordering as shown by the good agreement obtained between the experimental values ofKuand those calculated using the pair‐ordering theory. At temperatures below 400 °C, the induced anisotropy was primarily the result of NiFe long‐range order for film compositions between 44% Ni and 70% Ni. The results of anisotropy energy measurements for these films indicate the following: (i) the critical temperature for NiFe orderTcis composition dependent and agrees with the values obtained for neutron bulk‐irradiated samples; (ii) the NiFe order mechanism may be governed primarily by single vacancy diffusion; and (iii) the maximum value ofKuobtaind belowTcprobably depends more on the irradiation rate (flux) than fluence.