Background: Acute gastrointestinal injury (AGI) has been documented in critically ill patients, yet there remains a dearth of knowledge regarding its occurrence, predisposing factors, and outcomes in elderly polytrauma patients, a significant but overlooked population. This study aims to examine the frequency, risk factors, and clinical implications of AGI in elderly polytrauma patients. Methods: A retrospective, observational, multicenter study was carried out in two Level I trauma centers, encompassing a cohort of 1054 polytrauma patients from July 2020 to April 2022. Results: A total of 965 consecutive polytrauma patients were recruited who were divided into youth group (n=746) and elderly group (n=219). 73.5% of elderly patients after polytrauma were accompanied by AGI. An increasing ISS (OR=2.957, 95%CI: 1.285-7.714), SI (OR=2.861, 95%CI: 1.372-5.823), serum lactate (OR=2.547, 95%CI: 1.254-5.028), IL-6 (OR=1.771, 95%CI: 1.145-8.768), APTT (OR=1.462, 95%CI: 1.364-4.254) and a decreasing GCS (OR=0.325, 95%CI: 0.116-0.906) were each associated with an increasing risk of AGI in elderly polytrauma patients. Elderly polytrauma patients with AGI were presented relatively high 28-day mortality (40.4%) and super high 60-day mortality (61.2%) compared with elderly group without AGI and youth group with AGI. The area under the curve for predicting 28-day mortality in elderly polytrauma patients with AGI was 0.93 for AGI-III,IV with 96% sensitivity and 87% specificity. Conclusion: Elderly patients have a higher incidence and a worse prognosis of AGI after polytrauma. ISS, GCS, SI, serum lactate, IL-6, and APTT are identified as reliable prognostic markers to distinguish the AGI and N-AGI in elderly polytrauma patients. AGI-III,IV was the independent predictor of mortality in elderly polytrauma patients with AGI.