Early identification of ICU patients with sepsis who are at risk of early death remains clinically important. The aspartate aminotransferase-to-platelet ratio index (APRI) is a simple laboratory-derived index, but its clinical value for very early mortality in adult ICU patients with sepsis remains insufficiently characterized. This study evaluated the association between admission APRI and short-term mortality in ICU patients with sepsis. This retrospective cohort study included 266 adults admitted to the ICU with sepsis. APRI was calculated from AST and platelet measurements obtained within 24 h of admission. Patients were categorized according to mortality timing. Associations with 7-day mortality were evaluated using logistic regression adjusted for age, sex, and comorbidity status. ROC and survival analyses were also performed. Of 266 patients, 32 died within 7 days, 88 between 8 and 28 days, and 72 after 28 days, and 74 survived. APRI was highest among patients who died within 7 days (median 1.919, IQR 0.631–5.009) compared with survivors (0.472, IQR 0.192–1.531; p = 0.0056). Higher log-transformed APRI remained associated with 7-day mortality after adjustment for age, sex, and comorbidity status (OR = 2.77, 95% CI 1.57–5.01; p = 0.0004). APRI showed modest discrimination for 7-day mortality (AUC = 0.687, 95% CI 0.580–0.793) and lower discrimination for 28-day mortality (AUC = 0.623, 95% CI 0.555–0.690). Elevated APRI was also associated with reduced short-term survival. Elevated admission APRI is independently associated with early mortality and reduced short-term survival in ICU patients with sepsis. However, its modest discrimination supports its use as an adjunct to established clinical risk assessment tools.