The formation of co-amorphous combination of drug-excipient has proved to be a powerful approach to increase the dissolution of poorly water-soluble drugs. In the present study, four novel co-amorphous combinations of beta-azelnidipine (beta-AZE) and maleic acid (MAL) with the molar ratio of 1:1 and 1:2 were prepared by neat powder grinding (NG) and solvent-assisted grinding (SG) procedures, respectively. The obtained co-amorphous combinations were characterized by powder X-ray diffraction (PXRD), cryo-field emission scanning electric microscope (SEM), differential scanning calorimetry (DSC), Fourier-transform infrared (FT-IR), solid-state nuclear magnetic resonance (ssNMR) and terahertz (THz) spectroscopy. The PXRD technique confirmed the amorphous feature of these resultant combinations, and DSC technique was employed to access the glass transition temperature (Tg). The IR and ssNMR spectroscopy suggested the existence of hydrogen bonds of N-H center dot center dot center dot O (N-H in beta-AZE center dot center dot center dot O=C in MAL) and C-H center dot center dot center dot O (C-H in beta-AZE center dot center dot center dot O=C in MAL) in co-amorphous. Meanwhile, two heterogeneous dimers and one trimer were obtained using simulated calculation, in which existence of another type of hydrogen bond of O-H center dot center dot center dot O (O-H in MAL center dot center dot center dot O=N in beta-AZE). Interestingly, simulation suggests that two configurations may exist in one beta-AZE/MAL 1:1 dimer. The THz spectrum revealed that four beta-AZE/MAL combinations showed different vibration mode compared with the starting components and own the same type of intermolecular interactions. The solubility in different media and the dissolution rate in 0.1 mol/L HCI for four co-amorphous were determined; the dramatically improved dissolution rate of the beta-AZE/MAL 1:2 (SG) combination in vitro showed potential to improve the physicochemical properties of beta-AZE by co-amorphous. (C) 2015 Elsevier B.V. All rights reserved.