Introduction: Tiliacora triandra (F. Menispermaceae) is edible and is also known for medicinal values. The leaves are a popular flavoring in Southeast Asia, especially in the northeast of Thailand. The objectives of this study were to determine the major constituents of the leaves of T. triandra, and assess their anticancer activities against human cancer cell lines. Methods: The leaves were extracted by a soxhlet apparatus with petroleum ether, dichloromethane, ethyl acetate and water. Major constituents were then purified and identified using chromatographic procedures and various spectroscopic techniques. In vitro anticancer activity tests of T. triandra extracts were performed by resazurinmicroplate assay (REMA), and tested with 3 cell lines: oral cavity cancer (KB), lung cancer (NCI-H187) and breast cancer (MCF-7) cell lines. Results: The result indicated that the main compound of T. triandra leaves was oxoanolobine. The methanol extract showed the highest cytotoxic activity against lung cancer (NCI-H187) cell line whereas the water extract exhibited the highest activity against oral cavity cancer (KB) cell line. The IC50 of oxoanolobine against the NCI-H187 cell line was 27.60 ± 4.30 µg/mL. Conclusion: T. triandra leaves contain oxoanolobine as the major constituent and have the potential of anticancer activity but are required to be investigated further.