Abstract:The kelp off-cuts was used as raw materials.The ultrasonic-assisted extraction of fucoidan from kelp off-cuts with acidizing fluid.Fucoidan was optimized using the response surface methodology.The results of onefactor-at-a-time experiments showed that provided the best stability for the proanthocyanidins under power ultrasonics 150 W and extraction two times.pH，liquid to solid ratio（mL/g），extraction temperature（℃），and ultrasonic time（min）were selected as independent variables，while the extraction yield of fucoidan（%）was taken as response variable.The optimization was carried out based on Box-Behnken experimental design by investigating the individual and combined effects of the four factors on the response variable.The optimum extraction conditions were determined as follows：pH was 1.60 water extract with solid-liquid ratio of 37 ∶1（mL/g）at 78℃for 71 min.Under these conditions，the fucoidan yield obtained was 33.86%with a relative error of 1.28%as compared with the model prediction of 34.30%indicating that these parameters are reliable.The experiment result was consistent with the prediction result.This research can provide a technical reference for fucoidan extraction from kelp off-cuts.