Self-assembled uniform 3D flowerlike β-Ni(OH)₂/γ-Ni(OH)₂ composite nano-microspheres with hollow interiors were successfully synthesized via a facile aqueous-ethanol mixed solvothermal method, using nickel sulfate as a precursor, urea as a precipitant, and dehydroabietic based phosphate diester sodium (DDPDS) as a surfactant. The prepared 3D flowerlike β-Ni(OH)₂/γ-Ni(OH)₂ composite nano-microspheres were tested as supercapacitors in a two-electrode cell with 6 mol/L KOH electrolyte. In addition, the influence of DDPDS concentration on the morphology and size of 3D flowerlike β-Ni(OH)₂/γ-Ni(OH)₂ composite nano-microspheres was studied at 180 ℃. X-ray diffraction (XRD), scanning electron microscopy (SEM), BET (Brunauer, Emmett and Teller) techniques, and equity default swap (EDS) were used to characterize the structure, morphology, and size of the as-prepared samples. Moreover, a possible formation mechanism of the 3D flowerlike β-Ni(OH)₂/γ-Ni(OH)₂composite nano-microspheres was proposed based on the effects of DDPDS concentration and reaction time. The surfactant micelles were used as soft templates to induce the self-assembly of nanosheets. The crystallinity of the 3D flowerlike β-Ni(OH)₂/γ-Ni(OH)₂ composite nano-microspheres improved with the increase of DDPDS concentration, and the morphology and size of synthetic nano-microspheres could be controlled.