A novel HPLC method was developed and validated for simultaneous determination of potassium guaiacolsulfonate and sodium benzoate in pediatric oral powder. In this method, an analytical C8 column maintained at 25°C was used for chromatographic separation with a mixture of methanol and 0.02 M solution of tetrabutylammonium sulfate as the mobile phase. The composition of mobile phase was varied using a gradient program including an initial hold time of 7 minutes with methanol content maintained at 20% (v/v), followed by a linear gradient in 5.5 minutes in which methanol content was increased from 20% (v/v) to 50% (v/v) and a final hold time of 2.5 minutes with methanol content maintained at 20% (v/v). The total flow rate of mobile phase was maintained at 1.0 mL per minute. The UV detection was performed at 280 nm. Injection volume was set at 20 µl. The method was fully validated in terms of specificity, linearity, precision, accuracy, and robustness according to requirements of current guidelines and was proved as reliable and suitable for the intended application.