Objective To investigate the prognostic value of dynamic blood lactate monitoring in patients with aneurysmal subarachnoid hemorrhage (aSAH).Methods We retrospectively reviewed 86 patients with aSAH who were admitted to our hospital from September 2015 to September 2016. These subjects were divided into favorable outcome group (58 cases) and unfavorable outcome group (28 cases) according to the Glasgow Outcome Scale score. The two groups were compared in terms of serum lactate on admission and at 0, 1, 3, and 5 days after microsurgery.Results The favorable outcome group had significantly lower serum lactate levels than the unfavorable outcome group on admission and at 0, 1, and 3 days after microsurgery (1.97±1.42/1.24±0.86/1.36±0.90/1.14±0.50 vs 3.20±1.54/1.98±1.11/2.28±1.58/1.73±1.23, P<0.05). The Hunt-Hess grade IV-V patients had significantly higher serum lactate levels than the Hunt-Hess grade I-Ⅲ patients on admission and at 0, 1, and 3 days after microsurgery (P<0.05). Binary logistic regression analysis showed that Hunt-Hess grade, Fisher grade, and serum lactate level at 3 days after microsurgery were prognostic factors (odds ratio=3.184, 95%CI:1.065-9.507, P=0.038).Conclusions In the acute stage of aSAH, dynamic blood lactate monitoring has great value in assessing disease condition and outcome; the blood lactate level at 3 days after microsurgery is an independent prognostic factor.