The effects of contezolid (MRX-I, an oxazolidinone antibacterial agent) on cardiac repolarization were evaluated retrospectively using a population modeling approach in a Phase I study incorporating single ascending dose, multiple ascending dose, and food effect assessments. Linear mixed effect models were used to assess the relationships between MRX-I plasma concentrations and QT/QTc/∆QTc (baseline-adjusted), in which different correction methods for heart rate have been included. The upper bound of the one-sided 95% confidence interval (CI) for predicted ∆∆QTc was < 10 ms (ms) at therapeutic doses of MRX-I. Model performance/suitability was determined using diagnostic evaluations, which indicated rationality of one-stage concentration-QT model, as well as C-QT model suggested by Garnett et al. The finding demonstrated that MRX-I may have no clinical effects on the QT interval. Concentration-QT model may be an alternative to conventional thorough QT studies.