Abstract: To determine the promoting effects of enzyme hydrolysis products of Larimichthys polyactis on the proliferation of Streptococcus thermophilus FUA329. The in vitro antioxidant activity of the enzymatic hydrolysis with different molecular weights were determined. Papain was selected for the enzymatic hydrolysis of its by-products on the basis of selecting different enzymes to hydrolyze the processing by-products of Larimichthys polyactis. Taking the proliferative effect of enzymatic degradation products on Streptococcus thermophilus as an indicator of evaluation. The enzymatic hydrolysis conditions were optimized through single factor and response surface methodology. The in vitro antioxidant activity of the hydrolysis products of the by-products of Larimichthys polyactis (HPBL) were determined. The results showed that the best enzymatic hydrolysis conditions included the hydrolysis time, material-liquid ratio and enzyme loading were 5 h, 1:5.1 (w/v) and 2.8% (w/v), respectively. The HPBL prepared under the optimized conditions was separated by ultrafiltration into four fragments, according to the molecular weight: >10000 Da, 5000~10000 Da, 3000~5000 Da, <3000 Da, among which the fragment with molecular weight of less than 3000 Da promoted the proliferation of Streptococcus thermophilus significantly. The scavenging rate of HPBL for DPPH, hydroxyl radicals and superoxide anion radicals reached 68.75%, 56.23% and 30.64%, respectively. The enzyme hydrolysis products of Larimichthys polyactis significantly promoted the proliferation of Streptococcus thermophilus FUA329 and showed antioxidant activity. HPBL would have a certain promoting effect on the proliferation of Streptococcus thermophilus FUA329, and a certain antioxidant capacity, which would have the potential to be developed as a nitrogen source for Streptococcus thermophilus.