The ratio of triglyceride (TG) to high-density lipoprotein cholesterol (HDL-C) is an objective approach to predicting poor outcomes in acute ischemic stroke (AIS). The impact of TG/HDL-C on hemorrhagic transformation (HT) after AIS remains unknown. The aim of this study was to explore the accurate effect of TG/HDL-C on HT after AIS. We enrolled a total of 1423 patients with AIS in the training cohort from a prospective, consecutive hospital-based stroke registry. Of the 1423 patients, HT occurred in 155 (10.89%) patients. The incidence of HT after AIS was significantly increased when there were low levels of TG (P=0.016) and TG/HDL-C (P=0.006) in patients with AIS attributable to large artery atherosclerosis (LAA), but not in those who suffered from cardioembolic stroke. After adjustment for covariates, a lower TG/HDL-C (OR=0.53, 95%CI=0.20-0.93) that was more than TG alone (OR=0.61, 95%CI=0.27-0.98) independently increased the risk of HT in LAA. Furthermore, our established nomogram indicated that lower TG/HDL-C was an indicator of HT. These findings were further validated in the test cohort of 558 patients with AIS attributable to LAA. In summary, a low level of TG/HDL-C is correlated with greater risk of HT after AIS attributable to LAA.