Abstract: OBJECTIVE To improve in vitro dissolution of resveratrol(RES) through preparation of RES-chitosan oligosaccharide(COS) amorphous solid dispersion(RES-COS ASD). METHODS The RES-COS ASD was prepared by ball milling, characterized by differential scanning calorimetry(DSC), X-ray powder diffraction(XRPD), scanning electron microscopy(SEM) and Fourier transform infrared spectroscopy(FTIR). The dissolution of RES-COS ASD was evaluated in vitro under sink and non-sink conditions, and the physical stability of RES-COS ASD was investigated. RESULTS DSC and XRPD indicated that RES-COS ASD was successfully prepared. SEM showed that RES-COS ASD was irregular, lumpy and granular, and the characteristics of RES and COS were disappeared. For RES-COS ASD(1∶4) and RES-COS ASD(1∶2), the saturation solubility of RES was significantly increased(P<0.01), which was 2.37 times and 2.29 times of raw materials, respectively. The dissolution rate of RES in the RES-COS ASD was significantly higher than that in pure RES at 20 min under sink condition (P<0.01). Besides, compared with pure RES, RES-COS ASD exhibited significantly improvement in vitro non-sink dissolution and maintained supersaturated degree for a long time. In addition, RES-COS ASD maintained physical stability for at least 6 months at 25 ℃ and 40 ℃. CONCLUSION RES-COS ASD prepared by COS combination of RES can effectively improve the dissolution of RES and maintain supersaturated dissolution.