Genistein (GEN) is an active pharmaceutical ingredient that presents the challenges of poor water solubility and low oral bioavailability. To tackle these challenges, a GEN solid dispersion was prepared by solvent rotary evaporation using polyvinylpyrrolidone K30 (PVP K30) as a carrier. The optimal formulation was determined by drug loading efficiency and in vitro release. The physical state of the solid dispersion was characterized by DSC, XRD, SEM and FT-IR. And the results of the in vitro release study indicate that the drug release of SD (1:7) increased 482-fold that of pure GEN at 60 min. Following oral administration to rats, the C_max and AUC_0–24 of SD (1:7) was increased 6.86- and 2.06-fold to that of pure GEN. The adipose fat index and body weight of the SD (1:7) group were significantly lower than those of the GEN group (p < 0.05). Meanwhile, the levels of TC and TG in the serum were significantly decreased in the SD (1:7) group compared with the GEN group (p < 0.05). All experiments revealed that solid dispersion could be a promising formulation approach to improve the dissolution rate, oral bioavailability, and effect on the reduction of lipid accumulation in high-fat diet-induced obesity mice.