Twenty-two compounds (1-22) were isolated from the stems and twigs of Garcinia schomburgkiana. NMR, IR, UV, and MS were used for structural elucidation, and comparisons were made with previous reports. Compound 1 exhibited the most potent α-glucosidase inhibition (IC50 0.31 ± 0.7 μM), outperforming the positive control (acarbose). Molecular docking results showed that the phenolic hydroxyl groups on the phenyl rings linked with active receptor sites on the protein in 1. By preventing the duplication of DNA sequences, Compound 1 is an excellent inhibitor of the α-glucosidase enzyme, and represents a potential novel class of α-glucosidase inhibitor.