White‐fungus‐like NiSx microspheres have been synthesized on a large scale by using a simple hydrothermal method. The influence of the reaction time and the surfactant on the final products was investigated, and the formation mechanism was discussed. The synthesized white‐fungus‐like NiSx microspheres were used firstly as fillers in the fabrication of NiSx/polyvinylidene fluoride (PVDF) composites. Relationships between the loadings of the NiSx and wave‐absorption properties of the composites were analyzed. The loss mechanisms of NiSx/PVDF with different loadings were also discussed according to their dielectric and magnetic behaviors.