Abstract: OBJECTIVE To investigate the enhancement of dissolution of sirolimus by its complexation with hydroxy- propyl-β-cyclodextrin. METHODS The inclusion complexes of sirolimus were prepared by ultrasonic method. The solubilizing power of hydroxypropyl-β-cyclodextrin were determined by phase solubility technique. X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FT-IR) and differential scanning calorimetry(DSC) were used to verify the formation of inclusion complexes. RESULTS Sirolimus and hydroxypropyl-β-cyclodextrin formed inclusion complexes. At 25 ℃, with hydroxypropyl-β-cyclodextrin concentration increased, the solubility of sirolimus rised from 1.18 mg·L^-1 up to 118.15 mg·L^-1, increased 100 times approximately. CONCLUSION Hydroxypropyl-β-cyclodextrin inclusion technology can rise the solubility of sirolimus significantly.