Fermented vegetable-based foods, renowned for their unique flavors and human health benefits, contain probiotic organisms with reported in vitro antioxidative effects. This study investigates the probiotic properties of Latilactobacillus sakei MS103 (L. sakei MS103) and its antioxidant activities using an in vitro oxidative stress model based on the hydrogen peroxide (H₂O₂)-induced oxidative damage of RAW 264.7 cells. L. sakei MS103 exhibited tolerance to extreme conditions (bile salts, low pH, lysozyme, H₂O₂), antibiotic sensitivity, and auto-aggregation ability. Moreover, L. sakei MS103 co-aggregated with pathogenic Porphyromonas gingivalis cells, inhibited P. gingivalis-induced biofilm formation, and exhibited robust hydrophobic and electrostatic properties that enabled it to strongly bind to gingival epithelial cells and HT-29 cells for enhanced antioxidant effects. Additionally, L. sakei MS103 exhibited other antioxidant properties, including ion-chelating capability and the ability to effectively scavenge superoxide anion free radicals, hydroxyl, 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid, and 2,2-diphenyl-1-picrylhydrazyl. Furthermore, the addition of live or heat-killed L. sakei MS103 cells to H₂O₂-exposed RAW 264.7 cells alleviated oxidative stress, as reflected by reduced malondialdehyde levels, increased glutathione levels, and the up-regulated expression of four antioxidant-related genes (gshR2, gshR4, Gpx, and npx). These findings highlight L. sakei MS103 as a potential probiotic capable of inhibiting activities of P. gingivalis pathogenic bacteria and mitigating oxidative stress.