Flower-like Ni nanoparticles in diameter of 200 approximately 250 nm were synthesized by a mild chemical solution method. They were composed of smaller single-crystal Ni grains with an average diameter of approximately 15 nm. XRD, EDS and HRTEM results show that these particles were mixed uniformly with iron oxide single crystals, which serve as seeds for the growth of the flower-like structure. And a possible growth mechanism was proposed. The transformer oil-based fluid with conductive Ni nanoflowers was prepared and the measurements indicate that the dielectric performance of transformer oil is improved using this sample as additive, which could attribute to their capability of electron scavenging.