Summary In this article, samples of white sufu were collected at different manufacture stages and their content of water‐soluble protein (WSP) and amino nitrogen (AN); the distribution of peptides in WSP and isoflavones, as well as the antioxidant activities, was analysed. Results indicated that the peptides with molecular weight of 500–1000 Da increased 13.09 times from 0.11 to 1.44 g 100 g−1 dry matter (DM) during the whole manufacturing, while isoflavone glucosides were almost entirely converted to aglycones after ripening for 15 days. Ferric reducing power (FRAP) and 2,2′‐azinobis‐3‐ethylbenzothiazoline‐6‐sulphonic acid radical scavenging activity (ABTS RSA) were significantly increased by 2.80‐ and 1.60‐fold, respectively. Correlation analysis suggested that ABTS RSA was significantly related to WSP (especially for the 500–1000 Da peptides; P < 0.01) and the content of aglycones (P < 0.05), while FRAP was only correlated to WSP (P < 0.05). It is concluded the peptides were the most important components contributing to the antioxidant activities of sufu.