Burn injuries can cause significant malnutrition, leading to cardiovascular impairments. The prognostic nutritional index (PNI) predicts postoperative complications. We evaluated the impact of preoperative PNI on major adverse cardiac events (MACE) after burn surgery. PNI was calculated using the equation, 10 × (serum albumin level) + 0.005 × (total lymphocyte count). Multivariable logistic regression analysis was conducted to evaluate the predictors for MACE at 6 months after burn surgery. Receiver operating characteristic (ROC) curve and propensity score matching (PSM) analyses were conducted. Additionally, Kaplan-Meier analysis was conducted to compare postoperative 1-year mortality between MACE and non-MACE groups. MACE after burn surgery occurred in 184 (17.5%) of 1049 patients. PNI, age, American Society of Anesthesiologists physical status, and total body surface area burned were significantly related to MACE. The area under the ROC curve of PNI was 0.729 (optimal cut-off value = 35). After PSM, the incidence of MACE in the PNI <35 group was higher than that in the PNI ≥35 group (20.1% vs. 9.6%, P <0.001). PNI <35 was related to an increased incidence of MACE (odds ratio = 2.373, 95% confidence interval = 1.499–3.757, P <0.001). The postoperative 1-year mortality was higher in the MACE group than in the non-MACE group (54.9% vs. 9.1%, P <0.001). Preoperative PNI was a predictor for MACE after burn surgery. PNI <35 was significantly related to an increased incidence of MACE. Moreover, MACE was related to higher postoperative 1-year mortality.