Macroalgae, such as red algae, green algae, and brown algae, as a substantial fraction of marine biomass are the main source for marine carbon cycling. The polysaccharides are the main components of the cell walls of algae, which have been widely applied in the food and medicine industries because of their various physiological activities (antitumor, antioxidation, antivirus, etc.). However, applications of the polysaccharides have been limited by their poor solubility and low bioavailability. The marine algae–degrading enzymes emerged as potential tools for hydrolyzing the polysaccharides into oligosaccharides with excellent solubility and biological activities. In this chapter, we will review the general properties of polysaccharide-degrading enzymes originating from marine bacteria, focusing especially on alginate lyases, agarases, and carrageenases, but also including fucanolytic enzymes and ulvan-degrading enzymes. The review concludes with an outlook toward potential future applications for preparing the functional oligosaccharides in the fields of food biotechnology and agriculture.