Biodegradable polymers, known as polysaccharides, are a significant class that exhibit a wide range of structures and have hydrophilic, biodegradable, non-toxic, and bioactive properties. Due to their substantial antitumor effects, they are the subject of current antitumor drug research. Aside from their inherent antitumor properties, several natural polysaccharides can be chemically changed to create highly stable, bioavailable, versatile composites that can deliver treatments to targeted tissues. As a result, there is a pressing demand for novel anti-cancer medications to address cancer treatment needs. Polysaccharides could be excellent options in this context. Polysaccharides have been shown in many research studies to possess anticancer properties, along with the human body, plants, animals, microbes, and marine creatures like algae are all rich sources of polysaccharides. They are addressed here from the perspective of targeted therapy because many researchers have essentially and clinically clarified their mechanisms of action. Overall, polysaccharide defensive strategies include boosting the effects of chemotherapy and directly targeting tumor cells. As targeted therapy involving marine polysaccharides evolves, these compounds may exhibit anti-cancer effects through the inhibition of tumor angiogenesis and the induction of apoptosis in tumor cells. Our focus will be on the utilization of polysaccharides in targeted therapy, encompassing their roles in drug delivery, gene delivery, and theranostics.