<p>Cancer remains one of the leading causes of mortality worldwide, with conventional chemotherapy limited by high cost, drug resistance, poor targeting, low bioavailability, and significant systemic toxicity. Advances in nanotechnology have improved the diagnosis and treatment of cancer by enhancing drug delivery efficiency and specificity. In this context, marine-derived polysaccharides such as fucoidan, alginate, chitosan, carrageenan, ulvan, laminarin, and hyaluronic acid have gained considerable attention due to their biocompatibility, biodegradability, low toxicity, and versatile physicochemical properties. These biopolymers serve as promising building blocks for nanocarrier systems, including nanoparticles, liposomes, micelles, and nanocapsules, which can overcome key limitations of conventional therapies by improving drug targeting, stability, and controlled release while reducing adverse effects. Additionally, their ease of chemical modification enables the development of advanced, stimuli-responsive delivery systems and supports structure–activity relationship studies. This review highlights the sources, properties, and biomedical applications of marine polysaccharides, with particular emphasis on their role in tumor-targeted drug delivery, along with current advancements and challenges in marine biopolymer-based nanocarrier systems.</p> Graphical Abstract <p></p>