The cardiothoracic ratio (CTR) and serum aluminum levels are both associated with mortality in hemodialysis patients. However, limited data regarding the association between serum aluminum levels and the CTR have been published to date. Therefore, we aimed to elucidate this association in patients on chronic hemodialysis (CHD). We investigated the association between the serum aluminum level and the CTR in CHD in a retrospective cross-sectional study of 547 Taiwanese patients on CHD. The mean age of patients was 62.5±13.2 years, with a mean hemodialysis time of 7.1±5.2 years. Among the patients, 36.9% were diabetic and 47.9% were male. After natural logarithmic transformation (ln(aluminum)), the serum aluminum level exhibited an independent and linear relationship with the CTR (β: 1.40, 95% confidence interval (CI), 0.6-2.2). A high serum aluminum level (≥6 ng/dL) was significantly associated with a CTR >0.5 in the crude analysis (odds ratio (OR): 2.15, 95% CI, 1.52-3.04) and remained significant after multivariable adjustment (OR: 2.45, 95% CI, 1.63-3.67). Moreover, the ln(aluminum) value was significantly associated with a CTR >0.5 (OR: 1.71, 95%CI, 1.28-2.29) in multivariable analysis, indicating a dose effect of aluminum on cardiomegaly. In conclusion, the serum aluminum level was independently associated with cardiac remodeling (elevated CTR) in patients on CHD.