The synthesis, crystal structure and magnetic properties of the title compound are presented: Fe[C5(CH3)5]2[Ni(III)(S4C3O)2](CH3CN), Mr = 786.65, crystallizes in the C2/m monoclinic space group with cell parameters a=16.374(4) Å, b=10.84(2)Å, c=19.530(5)Å, β=98.02(2)°, V = 3431 Å3, Z = 4, dcalc= 1.523 g.cm−3, Full-matrix least-squares refinements gave R(F) = 0.060, Rw(F) = 0.077 based on 1068 reflections with >3[sgrave](I). The magnetic behavior is typical of dominant ferromagnetic interactions to which very weak antiferromagnetic interactions are superimposed.