BACKGROUND Coma has been considered as a valuable symptom of heatstroke. This study aimed to evaluate the role of the Glasgow Coma Scale (GCS) as an indicator of prognosis of patients with heatstroke. MATERIAL AND METHODS From Jan 1st, 2013 to Dec 31st, 2020, the clinical courses of 257 heatstroke patients from 3 medical centers in Guangdong, China, were observed. Diagnosis of heatstroke was made according to Expert Consensus in China. GCSs were calculated on the 1st, 3rd, and 5th days after admission to intensive care units (ICUs). GCS £8, as a coma criterion, was employed to predict the outcomes. RESULTS Seventy-five patients (29.18%) were comatose at admission. Twenty-seven (10.50%) patients, including 24 (24/75, 32.00%) coma patients and 3 (3/182,1.65%) non-coma patients died during ICU stay (P<0.0001). Patients with GCS ≤8 had a 2-fold higher risk of death as compared with those with GCS >8. The area under curves (AUCs) of GCSs on the 1st, 3rd, and 5th days to predict mortality were 0.81 (0.70-0.91), 0.91 (0.84-0.98), and 0.91 (0.82-0.99), respectively. Each additional 1 year of age, 1/min of respiratory rate (RR), and 1% of hematocrit (HCT) increased the risk of death of coma patients by 3%, 6%, and 4%, respectively (all P≤0.05). Patients with improving GCSs had lower mortality rates than non-improving patients (5.71% vs 55.00%, P<0.0001) within 5 days after admission. CONCLUSIONS GCS ≤8 at admission predicted worse outcomes in heatstroke patients, which possibly enhanced the risks of death for other factors, including age, RR, and HCT.