Objective:To prepare the solid dispersion of daidzein (DZ) colloidal silicon dioxide (Aeroperl 300 Pharma, AP) (DZ-AP), and evaluate its promotion effects on oral absorption of daidzein in vivo and in vitro. MethodsThe formulation of DZ-AP was optimized by uniform design. Both differential scanning calorimetry (DSC) and X-ray diffraction (XRPD) were used to characterize DZ-AP. The cumulative dissolution rates and the changes of plasma concentration in rats were detected to evaluate the drug releasing of DZ-AP in vivo and in vitro, and the stability of DZ-AP solid dispersion was investigated.  Results:The formulation of DZ-AP solid dispersion was optimized by uniform design as follows:daidzein 100 mg was dissolved in 3 times amount of methanol, 300 mg APs was added, and stirred at room temperature for 45 minutes, evaporated and dried for 1 hour. The DSC and XRPD results showed that majority of the drug existed in amorphous state. The dissolution rate of DZ-AP was significantly faster than that of the raw drug in vitro. The rat pharmacokinetics data showed that the relative bioavailability of solid dispersion was 137.1 percent of raw daidzein. The results of stability test showed that there were no obvious changes in the content and dissolution of daidzein when DZ-AP was stored at room temperature and acceleration condition for 3 months, which indicated the good stability of DZ-AP during storage.  Conclusion:The preparation of DZ-AP solid dispersion with AP as carrier can effectively improve the dissolution rate and oral bioavailability of daidzein.