Introduction: Terminalia ferdinandiana Exell. is an endemic Australian plant which is known for its exceptionally high antioxidant content. The fruit is a nutritional food and the leaves and kinos were used in Australian Aboriginal medicine to treat a variety of diseases. However, T. ferdinandiana kinos remain largely unexamined for their medicinal properties. Methods: Solvent extracts were prepared from T. ferdinandiana kinos and their antiproliferative activities against G. duodenalis and were determined by direct enumeration. The anti-proliferative activities against HeLa and Caco2 cancer cell lines were determined using an MTS based cell assay. Toxicity was determined using the Artemia franciscana nauplii bioassay. Results: Methanolic and aqueous T. ferdinandiana kino extracts were strong inhibitors of Caco2 and HeLa cell proliferation, with IC50 values substantially below 1000 μg/mL. In contrast, the mid to lower polarity solvent extractions (ethyl acetate, chloroform and hexane) were less potent inhibitors of cell proliferation. The aqueous and methanolic extracts were also effective inhibitors of G. duodenalis proliferation, albeit with slightly higher IC50 values than against the Caco2 and HeLa cells. All T. ferdinandiana kino extracts were nontoxic in the Artemia franciscana bioassay, with LC50 values substantially >1000 μg/mL. Conclusions: The antiproliferative activity of the T. ferdinandiana kino extracts against G. duodenalis and the HeLa and Caco2 cancer cell lines indicates their potential in the treatment and prevention of giardiasis and some cancers.