QbD based Design of Experiments (DoE) approach was explored to study the effect of various factors influencing the optimisation of HPLC method for the simultaneous estimation of the four drugs viz. Ofloxacin (OFX), Ornidazole (ORN), Terbinafine hydrochloride (TBH) and Clobetasol propionate (CBP) in bulk drug and in cream formulation. A full factorial design was employed to study the factors which may affect the chromatographic separation of the four drugs, such as pH of the buffer, initial percentage of organic content (%BI) and gradient time (Tg). The optimal conditions obtained after applying the principles of QbD with good system suitability parameters for all four drugs were found to be at pH 2.6, %BI as 24% of acetonitrile and gradient time of 4 min. The optimal conditions were found to be in a good agreement with the experimental results. The HPLC method thus developed was validated using ICH guidelines and was applied for the assay of cream formulation. The percentage recoveries were found to be 99.74±0.39 for OFX, 98.72± 0.71 for ORN, 98.19 ±0.23 for TBH and 99.05 ±0.76 for CBP. The HPLC method was successfully applied to study the in vitro permeability of cream formulation in rat skin using Franzch diffusion cell.