A new RP – HPLC method was developed for the simultaneous determination of  Montelukast and Rupatadine fumerate in combined dosage form. An Inertsil C18 column(100 x 4.6, 5µm) was used with mobile phase of composition Methanol : Buffer(0.1% triethyl amine in water with pH adjusted to 3.0 (70:30v/v at pH 4.6) at a flow rate of 1.0 mL/min and injection volume of 20µL with UV detection at 266 nm for separating Montelukast and Rupatadine fumerate. The retention time of Rupatadine fumerate and Montelukast were 5.76 min and 2.86 min respectively. The runtime of the analysis was 6 minutes. The specificity, linearity, precision, accuracy, limit of detection (LOD), limit of quantification (LOQ), ruggedness and robustness of the developed method were studied to validate as per ICH guidelines. The Linearity range for Montelukast and Rupatadine fumerate were 5.0 – 30.0 µg/ml and 5.0 – 30.0 µg/ml, respectively. The percentage recoveries were in the range for Montelukast and Rupatadine fumerate98.80-100.11 % and 99.06-99.44 %, respectively. The developed  method could be used for routine analysis of Montelukast and Rupatadine fumeratein their combined dosage forms.