Abstract: Abstract: In order to obtain fuco-oligosaccharides which possessed centralized molecular weight and remarkable bioactivity, an enzymic degradation method, due to its mild reaction conditions and no destructive effect on the structure of fucoidan, was adopted in this work. So the fucoidan lyases, derived from hepatopancreas of abalone (Haliotis diversicolor supertexta), were isolated and partially purified to hydrolyze fucoidans which were derived from Laminaria japonica. According to the electric properties of protein, an organic solvent method, an ammonium sulfate precipitation method and an isoelectric precipitation method were employed to isolate and purify the fucoidan lyases, and their purification effects were compared. First, for the isoelectric precipitation, the enzymic activity of precipitates at pH value 3.0 to 9.0 were measured with the viscometric method, aiming to shrink the isoelectric range of fucoidan lyases. The results showed that the precipitate at pH value 5.0 condition exhibited observably (p<0.05) higher enzymic activity than the other ones. It was indicated that the isoelectric point of fucoidan lyases ranged from pH value 4.0 to 6.0. Then the enzyme activity of precipitates which were obtained by the methods of isoelectric precipitation at pH value 4.5, 5.0, and 5.5, ammonium sulfate precipitation, and organic solvent, were measured with the DNS method. Finally, the results indicated that the crude fucoidan lyases had the highest enzymic activity at pH value 4.5 and 5.0, and that the enzyme activity recovery rates of the fucoidan lyases were 44.4% and 42.5%, respectively. Meanwhile, the content of sulfate groups of the hydrolyzed products (fuco-oligosaccharides) at pH value 4.0 to 6.0 were measured. The results showed that there were no significantly (P>0.05) decrease of sulfate groups for the fuco-oligosaccharides compared with that of the original fucoidans, which implied that no sulfatase existed in the crude fucoidan layses at pH value 4.5 and 5.0. Due to the better enzymic activity of the crude fucoidan layses precipitated at pH value 4.5 and 5.0, their enzymology characteristics were further discussed. The results displayed that the optimum hydrolysis reaction conditions were 2 g/mL of substrate concentration for 60 min at 38℃. Then the crude fucoidan layses were further isolated and purified with an ammonium sulfate precipitation and gel filtration chromatography. The results showed that when the saturation of ammonium sulfate reached 30% and 40%, the crude fucoidanase and α-L-fucosidase were obtained, respectively. In the end, the results indicated that the enzyme activity of fucoidanase was 0.43 U and α-L-fucosidase was 0.27 U after gel filtation. The enzyme activity recovery rate of the two fucoidan lyases were both 16%, which manifested that the enzymic activity of fucoidan lyases had a loss in the process of isolation and purification. The experimental results showed that two kinds of fucoidan lyases could effectively degrade fucoidans whose degration rates were 8%-15%, and that the sulfate groups of fucoidans were not obviously destroyed. Consequently, low molecular weight oligosaccharides (Fuco-Oligosaccharides) were produced, and the relative binding rate of sulfate groups were maintained at over 85%. Therefore, the fucoidan lyases from hepatopancreas of abalone might be used as a tool enzyme to hydrolyze high molecular weight fucoidans, and can have an important application value in the market in the future.