BACKGROUND: Polysaccharides from algae provide a range of biology and health benefits. Lately, there has been a significant interest in how algal polysaccharides affect the immune microenvironment around tumors. PURPOSE: To elucidate the subtle interactions between algal polysaccharides and the tumor immune microenvironment to further understand the medicinal potential of algal polysaccharides. STUDY DESIGN: To give a summary of the sources, bioactivities and characteristics of the tumor immune microenvironment of algal polysaccharides, and to analyze alteration of the immunological milieu surrounding tumors by algal polysaccharides and their potential as immunomodulators of chemotherapeutic agents. METHODS: Search popular academic search engines using selected keywords for articles ending before September 2024 using selected keywords Google Scholar, PubMed, ScienceDirect, Scopus, Web of Science, Springer, and official websites. RESULTS: Algal polysaccharides can fight tumors by changing how immune cells work and affecting inflammation in different ways. Moreover, algal polysaccharides have shown promise in mitigating the adverse effects associated with conventional cancer treatments, such as chemotherapy. Algal polysaccharides, through their immunomodulatory effects, can alleviate some of these side effects, leading to an enhanced overall treatment outcome. CONCLUSION: As research continues to uncover the underlying mechanisms of their antitumor effects, algal polysaccharides are poised to become a vital component in the development of novel cancer treatments, providing new hope for patients and advancing the field of oncology.