Abstract: Objective：To investigate the relationship between serum levels of oxidized lipoprotein (a) ［ox-Lp(a)］ and the severity of cerebral ischemic stroke (CIS). Methods：Serum samples were collected from 93 CIS patients, including 45 severe CIS and 48 mild CIS, 30 patients with cerebral hemorrhage and 48 healthy controls. Then, the ox-Lp(a) and lipoprotein (a) ［Lp(a)］ levels in serum were measured and compared. Results：Both serum ox-Lp(a) and Lp(a) levels in the severe and mild CIS patients were significantly higher than those in healthy controls (all P<0.05). The serum levels of ox-Lp(a) and Lp(a) in the severe CIS patients were significantly higher than those in the mild CIS patients and the patients with cerebral hemorrhage (all P<0.05). The serum ox-Lp(a) levels were positively correlated with Lp(a) levels (r=0.429, P<0.01), and negatively with HDL-C levels (r=-0.149, P<0.01) in CIS patients. The National Institutes of Health Stroke Scale (NIHSS) scores in CIS patients were positively correlated with ox-Lp(a) (r=0.324, P<0.01) and Lp(a) levels (r=0.299, P<0.01). The multiple linear regression analysis showed that both ox-Lp(a) (β=0.246, P=0.031) and Lp(a) (β=0.243, P=0.033) accounted for 13.6% of the variation in NIHSS (R²=0.136). The multiple logistic regression analysis showed that serum ox-Lp(a) was the potential risk factor of severe CIS after adjusting for age, sex and plasma lipid levels (OR＝1.209, 95% CI＝1.033~1.414). Conclusion：There were increased serum ox-Lp(a) levels in CIS patients, which was related to the severity of CIS.