Background: Terminalia spp. are characterised by their high antioxidant capacities and many have anticancer activity. This study examines the anti-proliferative activity of T. carpentariae leaf and T. grandiflora leaf, fruit and nut extracts against Caco-2 and HeLa carcinoma proliferation. Materials and Methods: Powdered T. carpentariae leaf and T. grandiflora leaf, fruit and nut were extracted and tested for anti-proliferative activity against Caco-2 and HeLa cancer cell lines using colorimetric cell proliferation assays. Toxicity was evaluated using an Artemia franciscana nauplii bioassay. The extract with the most potent anti-proliferative activity was examined using GCMS analysis and triterpenoid compounds were identified by comparison with a compound database. Results: T. carpentariae leaf and T. grandiflora leaf, fruit and nut extracts displayed potent anti-proliferative activity against Caco-2 and HeLa carcinoma cells. The methanolic T. grandiflora leaf extract was particularly effective at blocking the proliferation of the colorectal carcinoma Caco-2 (IC50 = 372 μg/mL). The methanol T. carpentariae and T. grandiflora leaf extracts were similarly potent inhibitors of HeLa cervical cancer cell proliferation with IC50 values of 864 and 833 μg/mL respectively. The methanolic T. grandiflora fruit and nut extracts, as well as all aqueous and ethyl acetate extracts, were moderate to good inhibitors of carcinoma proliferation. In contrast, chloroform and hexane extracts were generally devoid of anti-proliferative activity. The methanolic T. grandiflora extracts displayed low toxicity in the Artemia nauplii bioassay. All other extracts were non-toxic. GC-MS analysis of the methanolic T. grandiflora leaf extract identified 3 lanostane and 2 pentacyclic triterpenoids. Conclusion: The low toxicity and anti-proliferative activity observed with the T. carpentariae and T. grandiflora extracts against Caco-2 and HeLa indicate their potential for the prevention and treatment of some cancers.