Ulvan is a major component of the cell wall in green algae belonging to the genus Ulva. Ulvan lyases specifically degrade ulvan into related oligosaccharides. These enzymes cleave the (1→4) glycosidic linkage at the non-reducing end of uronic acid residues to form 4-deoxy-l-threo-hex-4-enopyranosiduronic acid at the non-reducing end of the oligosaccharide products. Based on the similarity of protein sequences, ulvan lyases are classified into five polysaccharide lyase (PL) families, namely PL24, PL25, PL28, PL37, and PL40. The elucidation of their structures, biochemical properties, and catalytic mechanisms is essential for promoting the high-value utilization of green algae. Herein, we have summarized the recent research progress on the identification and biochemical characterization of ulvan lyases. Additionally, the structure features, catalytic mechanisms, and applications of ulvan lyases have been described. This comprehensive information will be helpful for the extensive applications of the enzyme in various industries.