Abstract: Using pineapple peel as materials, optimal process conditions of ultrasound-assisted extraction of polysaccharides and its antioxidant activities were studied. Based on the single factor experiment, orthogonal experiment was conducted to optimize the extraction process. The antioxidant activities in vitro were also evaluated in three systems with hydroxyl radical (·OH) scavenging capacity, DPPH free radical ( DPPH·) scavenging capacity and reducing capacity.The optimum conditions of pineapple peel polysaccharides were determined as follows: material to liquid ratio was 1 ∶ 50, extraction time was 40 min, extraction temperature was 60 ℃, ultrasound power was 60%.Under the optimal conditions, the extraction yield was 2.38%.The scavenging rate on hydroxyl radical ( ·OH) of the polysaccharides from pineapple peel increased with the increase of polysaccharides concentration ( 1.5 ~ 3.5 mg/m L) and was lower than VCat the same concentration. The polysaccharides from pineapple peel had good DPPH scavenging effect when compared with standard VCand the IC₅₀ on DPPH· was 2.47 mg/m L.The reducing capacity on Fe³⁺increased with the increasing concentration.So, the polysaccharides can be extracted effectively by this method and the polysaccharides have good antioxidant activities.The extraction of active polysaccharides from pineapple peel residue can realize the high value utilization of pineapple resources.