To elucidate the effects of sonication on the antioxidant activities of compounds in soy sauce, sonication at 68 kHz (60 W/L/10 min/8 circles) was employed during moromi fermentation. Sonication enhanced four antioxidant indices of soy sauce from 5.29% to 24.29%, which were attributed to the significantly higher levels of free amino acids (FAAs, 12.45%), total phenolics (26.71%) and 1–3 kDa peptides (12.28%) in sonicated moromi. Amongst them, FAAs contributed 65.88% and 53.45% to the enhanced metal ion chelating activity and DPPH radical scavenging activity (p < 0.05), respectively. However, Maillard reaction products and isoflavones contributed little to the enhanced antioxidant activities, because sonication slightly affected Maillard reaction products, isoflavones and β-glucosidase activities during moromi fermentation. It was concluded that cell wall of soybean was destroyed by sonication, facilitating the release of antioxidant compounds, which significantly enhanced the antioxidant activities in raw soy sauce. •Sonication significantly facilitated antioxidant compounds release.•Sonication remarkably improved antioxidant activities of soy sauce.•FAAs, phenolics, 1–3 kDa peptides increase led to antioxidant activities improvement.