Background and Objectives: The study aimed to explore the association between energy intake (EI), the proportion of enteral nutrition intake (EN%), and prognostic-related indicators. Methods and Study Design: This was a prospective observational study. Patients aged 18-80 years old, who had undergone cardiothoracic surgery, were enrolled between January 2017 and January 2018. The measured REE (mREE) was evaluated by indirect calorimetry (IC). The observational data on EI, EN% and EI/mREE% were collected following admission to ICU, ICU discharge, and prior to discharge. Results: A total of 160 patients (60.6% male) were studied. The pre-albumin and total protein were positively correlated with EN% at the time of ICU discharge; liver function index levels were negatively correlated with EI/mREE% at discharge (p＜0.05). Multiple linear regression indicated that ALT levels as well as EI/mREE% were related to the duration of mechanical ventilation; ALT, AST, APACHE II were related to the ICU duration; EN% and EI/mREE% were related to the length of stay (LOS) following ICU discharge. EN% was related to the LOS in the hospital. Conclusions: The patients treated cardiothoracic surgery demonstrated associations of EN% with LOS in the hospital. Increased EN% and EI/mREE% were associated with higher serum protein levels and maintain normal liver function.