Abstract Withanolides are the group of active chemical constituents of Withania somnifera (L.) Dunal. Withaferin A, withanolide A and withanone presents three of the biologically most active constituents of this herb. These steroidal lactones are isomers of each other and thus, pose significant difficulty in their separation. In present study, a simple, specific and reliable RP-HPLC method has been developed and validated for their separation and simultaneous quantification. Separation was carried out on Lichrocart Purospher STAR RP-18e column (250 × 4.5 mm, 5 µm) using mobile phase, methanol and 0.01 M ammonium acetate buffer (pH 5) in the ratio 60:40, v/v. The calibration curves were linear (r 2 > 0.99) for all the three compounds across concentration range of 1.56–50 µg/mL. The lower limit of quantification for all the analytes was 1.56 µg/mL. The intra-day and inter-day accuracy was between 88.65% and 110.66% and coefficient of variation was between 0.55 and 10.12. The analytes were stable under different storage conditions. The developed method was successfully applied to analyze the samples for simultaneous determination of permeability of the three withanolides in rats using in situ single-pass intestinal perfusion model. Withanolide A and withanone were found to be high permeability compounds while withaferin A could not be detected.