A fucoidanase, which was screened from the heptopancreas of Patinopectin yessoensis, was fractionated according to by ammounium sulfate precipitation and anion exchange chromatography. The crude fucoidanase activity was hydrolyzed a small amounts of fucoidan agar and not arrageenan. The crude enzyme hydrolyzed fucoidan to produce oligosaccha-rides of fucose, glucose, maltose maltotriose and maltoteraose as the reaction products.