Atomically smooth Co–Fe–Ta–B glassy films were deposited on variety of substrates (Si, SiO2, and keptone). An extensive magnetic characterization in the temperature range from 5 to 330 K is reported for the films of thickness up to ∼5.5 μm. A reversible spin reorientation transition (SRT) from in-plane single domainlike state to out-of-plane multidomain state with increase in measuring temperature from 5 to 330 K was observed in the films of thickness up to ∼2.5 μm, in contrast to previously reported ultrathin ferromagnetic films of transition metals consisting of about half a dozen of monolayers. The SRT temperature (TSRT) is dependent on the film thickness and the applied magnetic field and is not governed by the temperature dependent magnetocrystalline anisotropy or the anisotropy at the film-substrate interface, which are the most common cause for the SRT in magnetic materials. Atomic relaxation has significant influence on SRT. The relaxed state results in a shift in TSRT to higher temperature or disappearance of SRT. We have compared our results with the reported data on ultrathin ferromagnetic films and shown that the atomic randomness and the strains/stress are responsible for the SRT in present case.