Within the Hubbard model with allowance for Hund’s and spin–orbit interactions, the concepts of thermal spin fluctuations in a strongly correlated system of f electrons in PuCoGa_5 are developed. The effect of fluctuations of the spin magnetic moments of different orbitals on the spin–orbit splitting of the f electron spectrum is considered. The mean square magnetic moment obtained in this case makes it possible to describe the observed temperature dependence of the magnetic susceptibility (χ( T )) of PuCoGa_5 near and above the electron pairing temperature. Estimates of the radius of spin correlations correspond in order of magnitude to the sizes of Cooper pairs in superconductors with the d symmetry of the order parameter. In the high-temperature region, the magnetic susceptibility obeys the Curie–Weiss law. With decreasing temperature, when approaching the pairing temperature, the ferromagnetic instability is suppressed and the temperature maximum of χ( T ) appears.