Flower-like NiO microspheres with an average size of ⁓ 3 μm and nanoflakes size ⁓ 10–100 nm were synthesized by surfactant-assisted chemical precipitation method, using Ni(CH3CO2)2·4 H2O as a nickel source, diethanolamine as a complexing agent, and cetyltrimethylammonium bromide as a surfactant. The obtain material was characterized by SEM, EDX, HR-TEM, XRD, and TGA. The obtained results confirmed the formation of highly ordered flower-like NiO nanoparticles. The catalytic activity of the obtained material was evaluated in the epoxidation reaction of styrene under ambient conditions, using meta-chloroperoxybenzoic acid (m-CPBA) as an oxidant. The obtained results revealed an immediate conversion of styrene to styrene oxide, with high conversion (87%), medium selectivity (65%), and high turnover-frequency (TOF) (243 s−1). However, when bulk NiO was applied only 62% conversion with 68% selectivity and TOF = 174 s−1 were obtained. Furthermore, this catalyst is was easily separable and recyclable. Moreover, a possible reaction mechanism is also proposed.