This research explores the antiproliferative effects of short-chain fatty acid (SCFA) salts (magnesium acetate, sodium propionate, and sodium butyrate) on AGS gastric adenocarcinoma cells. Sodium butyrate (NaB) exhibited the most significant inhibitory impact. The study investigated synergistic interactions between NaB and the drug dexamethasone (Dex) using a combination index model. Dex and NaB at a 2:8 ratio showed strong synergy, surpassing mono treatments in inhibitory activity. NaB induced pro-oxidative effects, countered by Dex in combination. Cell population analyses indicated a shift towards apoptosis with Dex, NaB, and their combination. Proteomic analysis revealed downregulation of the oncogene TNS4, suggesting a potential mechanism for antiproliferative effects. These findings suggest NaB as a potential adjuvant therapy with Dex, prompting further exploration of combination therapies and molecular mechanisms, emphasizing the potential application of these postbiotics in gastric cancer treatment.