A robust, precise, sensitive, linear, and simple RP LC method coupled with UV for the determination of emtricitabine or 2',3'-dideoxy-5-fluoro-3'-thiacytidine (FTC) and its related substances is described. The method uses an RP C18 column (25 cm x 4.6 mm i.d.), 5 microm kept at a temperature of 35 degrees C. The mobile phases for gradient elution consist of ACN, phosphate buffer (pH 4.4), and water. The flow rate is 1.0 mL/min and UV detection is performed at 280 nm. A system suitability test (SST) was developed to verify the adequate performance of the chromatographic system. The developed method was further validated with respect to robustness, precision, sensitivity, and linearity. A central composite design was applied to examine the robustness of the method. The method shows good precision, sensitivity, linearity, and robustness. Three commercial FTC samples were examined using this method. This method is suitable to be used for the determination of related substances and assay of FTC.