A simple, rapid, and robust liquid chromatography method was developed and validated for the enantiomeric separation of duloxetine in bulk drug substance. The enantiomers of duloxetine were resolved on a Chiralpak AD-H (amylose based stationary phase) column using a mobile phase consisting of n-hexane-ethanol-diethyl amine (80:20:0.2, v/v/v) at a flow rate of 1.0 mL/min. The resolution between the enantiomers was found to be not less than 2.8 in optimized method. The presence of diethyl amine in the mobile phase played an important role in enhancing chromatographic efficiency and resolution between the enantiomers. The developed method was extensively validated and proved to be robust. The calibration curve for (R)-enantiomer showed excellent linearity over the concentration range of 750 ng/mL (LOQ) to 7500 ng/mL. The limit of detection and quantitation for (R)-enantiomer were 250 and 750 ng/mL, respectively. The percentage recovery of the (R)-enantiomer ranged between 98.3% to 101.05% in bulk drug samples of duloxetine. The proposed method was found to be suitable and accurate for quantitative determination of (R)-enantiomer in bulk drug substance.