Amomum tsao-ko is an important crop widely cultivated in China, whose dried fruits are popularly consumed as foods and medicines. In this study, the EtOH extract of the fruits of A. tsao-ko was first revealed with PTP1B selective inhibition. Under the guidance of bioassay, eight rare flavanol-menthane conjugates, amomutsaokins A–H (1-8), together with ten known phenolics (9-18), were isolated from A. tsao-ko. Their structures including absolute configurations were elucidated by extensive spectroscopic data (1D and 2D NMR, HRESIMS, IR and UV) and ECD calculations. Their antidiabetic potency against three diabetes-related proteins (PTP1B, TCPTP, and α-glucosidase) was evaluated, of which compounds 2, 3, 6, 14, and 16 exhibited PTP1B selective inhibition with IC₅₀ values of 201.45–317.51 μM, and compounds 1-3, 5-8, 10, and 16-18 displayed α-glucosidase inhibitory activity with IC₅₀ values ranging from 3.73 to 76.23 μM. Compounds 1 and 6 were demonstrated to be α-glucosidase mixed-type inhibitors with K_i values of 36.2 and 24.4 μM, respectively. Molecular docking suggested that compounds 1 and 6 were well located into the active site of α-glucosidase by interacting with W1355, W1369, K1460, F1559, H1584, and D1279 residues. This study enlightens the therapeutic potential of A. tsao-ko for the treatment of diabetes, as well as searching for new antidiabetic candidates from natural sources.