Bergenin (BER) is a bioactive compound used for the treatment of chronic bronchitis in China. However, its low solubility and permeation limits its oral bioavailability. In this study, a new BER: isonicotinamide (ISN) cocrystal (1: 1, molar ratio) was reported for the first time. BER-ISN shows better solubility and intrinsic dissolution rates (IDRs) in aqueous medias such as water, buffer solutions with pH = 1.2, 4.5, and 6.8 in comparison to BER monohydrate. For instance, the solubilities of BER-ISN and BER monohydrate in water were 3.72 ± 0.22 and 1.42 ± 0.006 mg/mL, respectively, showing 2.62 times improvement. IDRs of BER-ISN and BER monohydrate were 29.90 ± 0.04 and 18.64 ± 0.27 mg/min/cm2, respectively, which was consistent with the solubility results. To explain the solubility behavior, phase solubility diagrams of BER monohydrate, ISN and BER-ISN in three pure organic solvents (ethanol, isopropanol and ethyl acetate) were performed according to the solubility product (Ksp) and complexes formation (K11) theory. The predicted solubilities are consistent with experimental solubilities considering complexation effects. The Hildebrand solubility parameter (HSP) calculations support the results. Thus, BER-ISN cocrystal (1: 1) with improved solubility is a good candidate for further formulation development.