The present paper describes a simple gradient reverse phase HPLC method for the determination of two potential genotoxic Benzene-1,3-dicarboxaldehyde or m-isophthalaldehyde (PHA) and 3-(2-(7-chloroquinoline-2-yl)-(e)-vinyl) benzaldehyde (BNA) in Montelukast Sodium (MNK). Good resolution between two aldehydes PHA, BNA and Montelukast Sodium was achieved with Zorbax SB phenyl (150 mm × 4. 6mm, 3.5 µ) column using a gradient of buffer 2% trifluroacetic acid, pH adjusted to 1.9 and acetonitrile. The flow rate was 1.5 ml/min and the elution was monitored at 238 nm. The factors involved in the method development are discussed. This method was validated as per International Conference on Harmonization (ICH) guidelines and is able to quantitate two aldehydes at 0.25 ppm levels each with respect to 1.7 mg/ml of MNK. The method is linear in range of 0.125–0.30 ppm, which matches the range of 50–120% of estimated permitted level (150 ppm) of PHA and BNA were not present in the three studied pure batches of MNK