Abstract: The soluble dietary fiber (SDF) was extracted from brown algae by complex enzyme extraction. Firstly, the effects of different extraction conditions on the extraction rate of brown algae SDF were studied  by single-factor experiment,  and then the  response surface analysis was carried out to determine  the optimal conditions for enzyme extraction of brown algae SDF,  and  the physicochemical properties of obtained brown algae  SDF and its antioxidant activity were determined. The results show that  the optimal extraction conditions are  m(solid)∶V（liquid）=1∶25, enzymatic hydrolysis temperature of  55 ℃, enzymatic hydrolysis time of 75 min and 2.2% enzyme addition, the maximum  extraction rate of brown algae SDF is  38.15%, and the relative deviation is 2.23%. The water holding capacity and swelling capacity  of brown algae SDF are 24.6 g/g and 53.7 mL/g respectively,  1,1-diphenyl-2-picrylhydrazyl  radical 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl（DPPH.） radical clearance rate is  75.77%, and there is no significant difference between the control group and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid）（ABTS.） radical clearance rate when brown algae SDF mass ratio is 160 μg/g. 

Key words: brown algae,  , soluble dietary fiber,  , complex enzyme,  , physicochemical property,  , antioxidation