Porphyranases are a specialized class of glycoside hydrolases capable of cleaving porphyran, a sulphated galactan polysaccharide derived from marine red algae of the genus Porphyra. With the increasing interest in oligo-porphyrin for its bioactivities, enzymatic degradation has emerged as the most selective and environmentally sustainable strategy, surpassing chemical and physical methods in both efficiency and product specificity. Despite the structural complexity of porphyran, only six porphyranases with confirmed activity have been identified since 2010, primarily from marine bacteria and human gut microbes. These enzymes are categorized into GH16 and GH86 families and exhibit diverse biochemical properties, including substrate recognition modes, methyl group tolerance, and degradation patterns. Structural and mutational analyses of porphyranases such as PorA, PorB, and Por16C_Wf have revealed unique mechanisms of substrate binding and catalytic specificity. Notably, Por16C_Wf shows unprecedented activity toward methylated porphyran, broadening the application potential of these enzymes. This review provides a comprehensive overview of porphyranase discovery, characterization, and structure-function relationships, offering essential insights for their application in marine polysaccharide bioconversion and biotechnological innovation.