Abstract Gastrointestinal acute radiation syndrome (GI-ARS) poses a critical public health concern, necessitating the development of effective medical countermeasures (MCM). Here, we evaluated the therapeutic potential of a commercially available probiotic formulation using a human gut-on-a-chip model that mimics the physiodynamic intestinal microenvironment. Intestinal epithelial Caco-2 cells were subjected to 8 Gy gamma radiation, targeting the epithelial layer, the culture medium, or both.