To develop a novel, accurate, precise and linear reverse phase high performance liquid chromatographic (RP-HPLC) methods for quantitative determination of cefotaxime sodium (CFT) in bulk drug and CFT loaded nanoparticles. Different analytical performance parameters such as linearity, precision, accuracy, specificity, limit of detection (LOD) and limit of quantification (LOQ) were determined according to International Conference on Harmonization ICH Q2B guidelines. The RP-HPLC method was developed by the isocratic technique on a reversed-phase Zorbax C18 (250 × 4.6 mm, 5µm) column with mobile phase consisting of phosphate buffer (pH7.4): acetonitrile (80:20v/v) at flow rate of 1.2 ml/min. Detection was carried out using a UV detector at 254nm. The retention time for CFT was 6.580+0.5min. The standard curve was linear over the concentration range of 10-50μg/ml with r2 close to one (0.999). The limit of detection (LOD) and limit of quantitation (LOQ) obtained for CET were 0.100μg/ml and 0.314μg/ml respectively. The developed and validated method was successfully applied for the quantitative analysis of nanoparticle. The high recovery and low relative standard deviation confirm the suitability of the proposed method for determining the assay and in vitro dissolution of a marketed formulation.