Objective To investigate the correlation of low-density lipoprotein cholesterol/lymphocyte (LDL-C/LYM) ratio with carotid plaque stability and stenosis in patients with acute ischemic stroke (AIS). Methods The study was conducted on 336 AIS patients treated in the Department of Neurology of Qinghai Provincial People′s Hospital from April 2021 to April 2022. According to the results of ultrasound examination, they were divided into non-plaque group (n=42), stable plaque group (n=63), and vulnerable plaque group (n=231). Based on the severity of stenosis, they were also assigned into non-stenosis group (n=42), mild (n=177), moderate (n=67) and severe stenosis group (n=50). The general data, LDL-C level, lymphocyte count, and LDL-C/LYM ratio were compared among different groups. SPSS statistics 23.0 was used for data analysis. Student′s t test, Kruskal-Wallis H test or Chi-square test was employed for intergroup comparison depending on different data type. Spearman correlation analysis was adopted to analyze the correlation between LDL-C/LYM ratio and severity of carotid stenosis, and multivariate logistic regression analysis was performed for risk factors of plaque vulnerability. Results Older age, larger proportions of hypertension and diabetes mellitus, and higher D-dimer and LDL-C/LYM ratio were observed in the stable and vulnerable plaque groups than the non-plaque group (all P<0.05). The vulnerable plaque group had larger proportion of diabetes mellitus, higher total cholesterol and LDL-C levels, and increased LDL-C/LYM ratio, but lower lymphocyte count when compared with the stable plaque group (all P<0.001). Multivariate logistic regression analysis showed that diabetes mellitus and LDL-C/LYM ratio were independent risk factors for carotid plaque vulnerability (OR=1.948,95%CI 1.01-3.77, P=0.048; OR=4.543,95%CI 1.10-18.69, P=0.036). Receiver operating characteristic (ROC) curve analysis indicated that the area under the curve (AUC) of LDL-C/LYM ratio for diagnosing plaque stability was 0.676 (95%CI 0.605-0.748; P<0.001), the optimal critical value was 1.54, the sensitivity was 61.5%, and the specificity was 69.8%. Spearman correlation analysis suggested that LDL-C/LYM ratio was positively correlated with the severity of carotid stenosis (r=0.654; P<0.001). Conclusion Increased LDL-C/LYM ratio is an independent risk factor for carotid plaque instability, and is positively correlated with the severity of carotid stenosis in AIS patients.