Objective To investigate the changes in serum homocysteine (Hcy) level and apolipoprotein B/A1 (ApoB/ApoA1) ratio in elderly patients with acute cerebral infarction (ACI) and their correlation with carotid intima-media thickness (IMT).Methods A total of 252 elderly patients with ACI were enrolled as case group, and according to carotid IMT, these patients were divided into normal IMT group with 65 patients, IMT thickening group with 87 patients, and carotid plaque formation group with 100 patients. According to serum Hcy level, the patients were divided into low Hcy group (Hcy ≤10 μmol/L) with 85 patients and high Hcy group (Hcy >10 μmol/L) with 167 patients. A total of 190 subjects who underwent physical examination were enrolled as control group. The groups were compared in terms of serum Hcy level, ApoB/ApoAl ratio, blood lipids, and carotid IMT. The multivariate logistic regression analysis was performed to analyze the influencing factors for carotid IMT thickening, and Pearson correlation was used to analyze the correlation of serum Hcy level and ApoB/ApoAl ratio with carotid IMT.Results The case group had significantly higher serum Hcy level, ApoB/ApoAl ratio, and carotid IMT than the control group (P<0.05). Compared with the normal IMT group, the IMT thickening group had significant increases in serum Hcy level, ApoB/ApoAl ratio, and low-density lipoprotein level (P<0.05), and the carotid plaque formation group had significantly greater increases (P<0.05). The high Hcy group had significantly higher serum Hcy level, ApoB/ApoAl ratio, and carotid IMT than the low Hcy group (P<0.05). The multivariate logistic regression analysis showed that Hcy (odds ratio [OR]=5.138, 95% confidence interval [CI] 3.862-8.825) and ApoB/ApoAl ratio (OR=4.742, 95% CI 3.571-7.283) were the risk factors for carotid IMT thickening. The correlation analysis showed that serum Hcy level and ApoB/ApoA1 ratio were positively correlated with carotid IMT in elderly patients with ACI (r=0.672, P<0.001; r=0.538, P=0.012).Conclusions Serum Hcy level, ApoB/ApoA1 ratio, and carotid IMT are associated with the development of atherosclerosis in elderly patients with ACI, and Hcy level and ApoB/ApoA1 ratio are risk factors for carotid IMT thickening.