It is known that malnutrition in acute ischemic stroke(AIS) patients is closely related to poor prognosis. The clinical and prognostic significance of the prognostic nutritional index (PNI), defined by Onodera et al, in patients with AIS has not yet been exhibited clearly. For this reason, our aim in this study is to determine the effect of PNI on short-term mortality of patients with AIS. Method: Our study was a single-centered retrospective study. The patient group consisted of 452 patients who were referred to our clinic within the first 24 h of symptoms and diagnosed with AIS between January 2010-2020. The patient and control groups were compared in terms of albumin, lymphocyte count(LC) and PNI levels. Results: Albumin, LC and PNI levels were lower in the patient group. Then the patient group was divided into two subgroups according to 30-day mortality [the first group (surviving patients(n=351)), the second group(exitus within 30 days after AIS(n=101))]. When these two groups were compared in terms of LC, albumin and PNI levels, the LC, albumin and PNI levels were found lower in the second group(p<0.05). A multivariate analysis to determine the risk factors associated with 30-day mortality after AIS revealed that uric acid and PNI were independent variables. Operating characteristic curve analysis also showed that values below 48 for PNI could be used with high sensitivity and specificity in detecting 30-day mortality due to AIS. Conclusions: This study showed that low PNI levels was closely associated with short-term mortality after AIS. Based on these results, it can be concluded that PNI levels may be regarded as a new indicator for determining post-AIS prognosis. More detailed and extensive prospective studies in this regard are needed in the future.