Frequency selective surfaces (FSSs) have been successfully used in constructing microwave absorbers which demonstrate the ability of modifying and improving its absorbing performances. In this paper, microwave absorber based on ferromagnetic nano-films has been proposed and investigated with a structure similar to that of the Salisbury screen except that the resistive sheet is replaced by FSS of square patch array of the nano-film. We have explored the FSS absorber from three aspects: equivalent circuit model, electromagnetic full-wave simulation and the actual sample measurement. By carefully tuning the patch size, the thickness of the dielectric spacer and the specification of the ferromagnetic nano-film, we obtain the optimized performance of broadband microwave absorbing. Due to the light weight of the nano-films, the proposed absorbers can achieve an ultra-low surface density less than 0.25 kg/m².