Abstract: The amaranth seeds were treated with steam explosion at different pressures(0.3,0.6,0.9,1.2,1.5 MPa)and different residence times(10,20,30,60,120 s). In order to explore the effect of steam explosion pretreatment on amaranth seeds,the total phenolic and flavonoid content were determined,with DPPH and ABTS⁺ radical-scavenging capacities,and ferric ion reducing power. The results showed that the total phenolic content,total flavonoid content and antioxidant capacity were significantly increased after steam explosion pretreatment(p<0.5). Under the optimal condition,pressure 0.6 MPa and time 60 s,the total phenolic content and total flavonoid content were 5.3 times and 7.3 times as much as that of the untreated sample respectively. Meanwhile,DPPH and ABTS⁺ radical-scavenging capacities,and ferric ion reducing power,were 4.6,3.8 and 11.6 times respectively. Thus,steam explosion is an efficient and non-polluting pretreatment,which would be useful for further development of amaranth seeds in the following.