Bioactive compounds play a significant role in disease prevention and maintenance of normal physiological functions. Numerous studies have identified antioxidant, anti-obesity, anti-cancer, anti-tumor, anti-viral, anti-angiogenic and neuroprotective activities of algal bioactive agents. This chapter discusses the health claims associated with marine algal bioactives and summarizes possible mechanisms involved in delivering health effects. Marine algae are important sources of valuable compounds capable of providing a plethora of biological activities. Algae have been traditionally used in several Asian countries viz. Korea, China and Japan for food and health purposes. Algae are considered an important source of biologically active substances due to their abundance and the advantage of environmentally friendly cultivation methods. Polysaccharides have prominent immunomodulatory and anticancer roles in pharmacological perspectives. Algal bioactive have been studied extensively for potential health benefits. Anti-viral polysaccharides from algae possess very low cytotoxic effects on mammalian cells. This attribute is of vital significance when using drugs as antiviral agents.