Soybean protein hydrolysates with a degree of hydrolysis of 14.1% were prepared by hydrolysis of soybean protein isolate with alcalase,and then modified by a plastein reaction in alcohol-water medium.Response surface analysis was applied to optimize the conditions of plastein reaction,when substrate concentration and reaction time were pre-set at 30% and 4 h.The suitable conditions obtained were as following: enzyme addition level of 5.26 kU/g proteins,volume ratio of ethanol to water of 56.8% and reaction temperature of 33.1℃.Some modified products with different reaction extents were prepared in ethanol-water or methanol-water medium,and their chelating activities for iron(II) and calcium(II) were evaluated.It was found that iron(II) chelating activity was increased from the original 39.8% to 59.3% while calcium(II) chelating activity was enhanced from the original 62.1% to 76.6%.The present results suggested that enzymatic hydrolysis coupled with plastein reaction might be served as a new approach to prepare iron soybean protein hydrolysates with better metal chelating activity.