This study evaluated the effects of supplementing sawdust medium with 10% (w/w) Korean-style soy sauce residue (KS) and brewed soy sauce residue (BS) on the cultivation of Pleurotus ostreatus. Over 25 days, KS treatment produced mycelial growth comparable to the control, whereas BS treatment showed slower colonization. Fruiting bodies appeared after nine days in the control, ten days with BS, and twelve days with KS, with fresh weights of 146.0 g, 174.8 g, and 89.0 g, respectively, indicating reduced yield with KS and increased yield with BS. In antioxidant assays, DPPH radical scavenging slightly increased from 89.15% in the control to 89.99% with KS and 90.34% with BS. ABTS scavenging was 82.36% in the control, 83.42% with KS, and 75.99% with BS. Total polyphenol content was 64.39 mg AAE/mL in the control, 62.72 mg AAE/mL with KS, and 43.28 mg AAE/mL with BS. In conclusion, KS supports mycelial growth without compromising DPPH-based antioxidant capacity, while BS enhances fruiting body yield but reduces ABTS activity and phenolic content. Both residues show potential as supplementary nutrients in conventional sawdust media.