Carrageenan　(CRG)　is　a　kind　of　linear　sulfated　polysaccharide　that　emerging　as　a　promising　substituent　in　food,　pharmaceutics,　and　cosmetics.　In　recent　years,　biological　properties　of　CRG　polysaccharides　such　as　antiviral,　immunomodulatory,　anticoagulant,　antioxidant,　and　anticancer　have　been　broadly　studied,　however,　systematical　summary　of　their　structure-property　relationships　is　scarce.　Moreover,　chemical　modification　is　of　great　significance　to　explore　biological　and　physiochemical　properties　of　CRG　polysaccharides　which　should　be　focused　on.　Chemical　modification　of　CRG　polysaccharides,　e.g.,　carboxymethylation,　thiolation,　acetylation,　phosphorylation,　oversulfation,　oxidization,　and　cationic　or　other　derivatives,　can　improve　their　bioactivities　and　facilitate　their　applications　in　different　biological　systems.　Hence,　this　review　aims　to　elucidate　structure-property　relationships　of　CRG　and　its　chemically　modified　derivatives　with　different　structures　and　bioactivities,　so　as　toxicity　of　CRG　as　food　additive　for　the　guidance　of　its　clinical　application.　©　2021　Elsevier　Ltd