It was unclear how nonconvulsive seizures (NCS) occurred after subarachnoid hemorrhage (SAH). The aim of this prospective observational study was to determine the association between cerebrospinal fluid postinfectious inflammation and NCS in patients with SAH. Demographics and parameters were retrieved from pooled data of all SAH patients monitored by continuous electroencephalography (cEEG) in our Stroke-Intensive Care Unit (Stroke-ICU) over six years period. Patients were divided into two groups (NCS group and non-NCS group). According to clinical and cerebrospinal fluid (CSF) parameters, a logistic regression model was used to analyze the association between CSF inflammation and NCS. The data of 143 SAH patients were analyzed (25 patients with NCS and 118 patients with non-NCS). Median age was 53 years (min - max: 19 years - 90 years). 4.8 % SAH patients were accompanied with NCS. Among these 25 NCS patients, only 2 (8%) had complete control of EEG discharges. After confounders correction, logistic regression analysis showed: SAH patients with older age [P = 0.003, OR = 1.193, 95 %CI (1.062-1.341)], intracranial infections [P = 0.000, OR = 171.939, 95 %CI (18.136-1630.064)] and higher increased modified Fisher Scale (mFS) [P = 0.003, OR = 8.884, 95 %CI (2.125-37.148)] were more likely to develop NCS; furthermore, a high level of CSF interleukin-6 (IL-6) was an independent risk factor for NCS [P = 0.000, OR = 1.015, 95 %CI (1.010-1.020)], with a threshold of 164.9 pg/mL (sensitivity = 0.84, specificity = 0.96). Compared with non-NCS patients, NCS patients were more likely to have poor Glasgow outcome scale (GOS) (1-3) at 3 months after discharge (88 %). SAH patients with NCS were associated with poor neurological prognosis. With the increase of age and mFS, these patients were more likely to develop NCS. As an intracranial infective mark, a high level of CSF IL-6 was an independent risk factor for NCS. For brain protection of severe brain injury after SAH, we should focus on the increasingly important role of inflammatory response. Copyright © 2020 Elsevier B.V. All rights reserved.