Background: Intramyocardial hemorrhage (IMH) is a result of ischemia-reperfusion injury in ST-segment elevation myocardial infarction (STEMI) after primary percutaneous coronary intervention (PPCI). Despite patients with IMH show poorer prognoses, studies investigating predictors of IMH occurrence are scarce. This study firstly investigated the effectiveness of regulatory T cell (Treg), peak value of Creatine Kinase MB (pCKMB), high-sensitivity C-reactive protein (hsCRP), and left ventricular end-systolic diameter (LVESD) as predictors for IMH. Methods: In 182 STEMI patients received PPCI, predictors of IMH were analyzed by logistic regression analysis. The predictive ability of risk factors for IMH were determined by receiver operating characteristic curves, net reclassification improvement (NRI), integrated discrimination improvement (IDI) and C-index. Results: Overall, 80 patients (44.0%) developed IMH. All 4 biomarkers were independent predictors of IMH [odds ratio [OR] (95% confidence interval [CI]): 0.350 (0.202–0.606) for Treg, 1.004 (1.001–1.006) for pCKMB, 1.060 (1.022–1.100) for hsCRP, and 3.329 (1.346–8.236) for LVESD]. After propensity score matching (PSM), the biomarkers significantly predicted IMH with areas under the curve of 0.750 for Treg, 0.721 for pCKMB, 0.656 for hsCRP, 0.633 for LVESD, and 0.821 for the integrated 4-marker panel. The addition of integrated 4-marker panel to a baseline risk model had an incremental effect on the predictive value for IMH [NRI: 0.197 (0.039 to 0.356); IDI: 0.200 (0.142 to 0.259); C-index: 0.806 (0.744 to 0.869), all p 0.05]. Conclusions: Treg individually or in combination with pCKMB, hsCRP, and LVESD can effectively predict the existence of IMH in STEMI patients received PPCI. Clinical Trial Registration: NCT03939338.