Introduction: Exposure to high levels of antioxidants has been linked to the treatment and prevention of some cancers. Although Cakile maritima has a high antioxidant capacity, it is yet to be tested for the ability to inhibit the proliferation of cancer cells. Methods: Solvent extracts prepared from C. maritima plant material were analysed for antioxidant capacity by the DPPH free radical scavenging assay. Anti-proliferative activities against CaCo2 and HeLa cancer cells were determined by an MTS based cell proliferation assay. Toxicity was determined by the Artemia franciscana bioassay. The most potent anti-proliferative extract (hexane) was further investigated using non-targeted GC-MS headspace analysis. Results: Good DPPH radical scavenging activity was calculated for all C. maritima extracts. The methanolic and ethyl acetate extracts had particularly strong antioxidant activity (IC 50 of 4.7 and 3.4 μg/mL respectively). Interestingly, the hexane extract which had the lowest DPPH radical scavenging activity (IC 50 13.6 μg/mL), was the most potent inhibitor or CaCo2 and HeLa carcinoma cell growth, with IC 50 's of 12 and 126 μg/mL respectively. The ethyl acetate extract was also a potent inhibitor of proliferation (IC 50 values of 185 and 468 μg/mL against CaCo2 and HeLa, respectively). The methanolic extract (IC 50 values of 2261 and 2046 μg/mL against CaCo2 and HeLa respectively) displayed only moderate anti-proliferative activity, demonstrating that antioxidant activity did not correspond with anti-proliferative activity. All of the extracts were determined to be nontoxic in the Artemia franciscana bioassay, with LC50 values substantially >1000 μg/mL. Non-biased GC-MS headspace analysis of the C. maritima hexane extract highlighted several interesting compounds that may contribute to the therapeutic bioactivities of the extract. Conclusion: The lack of toxicity and the anti-proliferative activity of the hexane and ethyl acetate C. maritima extracts against HeLa and CaCo2 cancer cell lines indicates their potential in the treatment and prevention of some cancers.