κ-Carrageenases belong to family 16 of glycoside hydrolases that degrade sulfated galactans in the red algae known as κ-carrageenans. A novel κ-carrageenase, named PLJ30, was cloned from Pseudoalteromonas carrageenovora ASY5. PLJ30 showed the highest activity at 45°C and pH 6.5. Its activity was impaired by most metal ions and reagents we tested. The ESI-MS analysis of hydrolysates showed that the degradation products are mainly disaccharides and tetrasaccharides, indicating that the enzyme is an endo-type carrageenase. It could be a valuable enzyme tool to produce carrageenan oligosaccharides. Practical applications Due to the higher viscosity of carrageenan, it is not easily be absorbed by the body, which greatly limits the application of carrageenan. Carrageenan oligosaccharides, which are the degradation products of carrageenan, are more easily absorbed by the organism and have a variety of biological activities such as antioxidation, antivirus, immunomodulation, and so on. At present, the preparation methods of carrageenan oligosaccharides mainly include physical, chemical, and enzymatic methods. Enzymolysis has the advantages of mild conditions, strong reaction specificity and less environmental pollution, thus slowly replacing the traditional preparation method of carrageenan oligosaccharides. It is difficult to produce carrageenase by direct fermenting strains isolated from nature, because of low yield, complex culture conditions, instable enzyme production, and high enzyme purification cost. Therefore, heterologously expressing the carrageenase gene isolated from nature by engineering method in order to increase the expression amount of carrageenase and achieve a large amount of preparation is of great importance for the large-scale preparation of carrageenase and the industrialization of carrageenan oligosaccharide.