In order to improve the foaming properties of soy protein isolate(SPI),transglutaminase(TGase) cross-linking was employed for the large(MW﹥10 ku) and small molecular peptides(MW﹤5 ku) that hydrolyzed from SPI with alcalase.The results demonstrated that: TGase cross-linking could effectively improve the foaming property of SPI,especially improve the foam stability effectively;for the large molecular peptide(MW﹥10 ku),the optimum foam stability(88.5%) was obtained with 15 U/g substrate of enzyme and 4 h of cross-linking time;as for the mixture of large molecular peptide(MW﹥10 ku) and small molecular peptide(MW﹥5 ku),the optimum foam stability(60.3%) could be obtained by 50 U/g substrate of enzyme,4 h of cross-linking time with 1∶ 1 molar ratio of large and small molecular peptide;the molecular weight of the cross-linking products from large molecular peptide(MW﹥10 ku) was higher than that from the mixture of large(MW﹥10 ku) and small(MW﹤5 ku) molecular peptide.The research may provide certain theoretical basis for improving the foaming property of SPI by enzymatic method.