A simple, sensitive and robust RP-HPLC method for the determination &quantification of related substances of Imipenem and Cilastatin in Reference Standard as well as in marketed formulation. The chromatographic separation was achieved with gradient elution by using Waters X terra MS (C18, 250 mm×4.6mm, 5.0µm column) with mobile phase composition of solvent A (pH 7.30 phosphate buffer and acetonitrile in the ratio of 98:2 v/v) and solvent B (pH 2.80 phosphate buffer and acetonitrile in the ratio of 68:32 v/v) at a flow rate of 1.0 mL/min and Column oven temperature 35°C. The analytes eluted were detected and quantified at 210 nm using photodiode array (PDA) detector. The specificity of the method was investigated under different forced degradation conditions, including hydrolytic, oxidative, photolytic and thermal as recommended by ICH guidelines. Robustness against small modification in pH, column oven temperature, flow rate and percentage of the mobile phase composition was ascertained. The method was developed and quantified in a manner indicating the stability and the sensitivity of the drug substance.