This article refers to simple isocratic reverse-phase high-performance liquid chromatographic method (RP-HPLC) developed for the simultaneous quantification of Escitalopram Oxalate (EST) and Clonazepam (CZP) in active pharmaceutical ingredient and pharmaceuticals. The separation of the two drugs was attained using a C₁₈ column (250mm×4.6mm, 5µ) as a stationary phase. The mobile phase was used as a mixture of methanol; acetonitrile; and 0.05M potassium dihydrogen orthophosphate buffer (pH 4 adjusted by orthophosphoric acid) with an isocratic ratio of 40:20:40 v/v. Detection was made by using PDA detector at 210 nm. Escitalopram Oxalate (RT= 4.428 minutes) and Clonazepam (RT= 6.532 minutes) were separated in a single chromatographic run with resolution of 8.719. The calibration plot indicated good linear relationship with r2 = 0.998 for Escitalopram Oxalate in concentration range of 32 µg/ml - 48 µg/ml and r2 = 0.999 for Clonazepam in concentration range of 16 µg/ml - 24 µg/ml. The retrievals for Escitalopram Oxalate and Clonazepam were found to be 99.75% and 99.00%, respectively. The established analytical method was validated and found acceptable as per ICH guidelines for linearity, precision, accuracy, specificity, limit of detection, limit of quantification, robustness and stability. Escitalopram Oxalate and Clonazepam individually as well as in combination were exposed to different stress conditions like acid, base, thermal, photolytic and oxidation degradation and peaks of a degraded product were well determined from peaks of pure drug. This method is modest, quick and appropriate for routine quality control analysis. Keywords: Reverse Phase – HPLC; Escitalopram Oxalate; Clonazepam; Validation; Degradation study.