A novel, sensitive, simple, rapid and economical method for the determination of the Guaifenesin in API and finished dosage formulations was validated using HPLC. Guaifenesin is a classical drug extensively used as an expectorant in symptomatic management of coughs, associated with the ability to loosen and thin sputum. Guaifenesin was dissolved in methanol and chromatographed on a c18 spherisorb (250cmX 4.5 mm, 5�m ).Detecton was performed on a JascoUV-975 detector with the mobile phase ratio of water:methano:acetonitrile(70:20:10v/v/v receptively).Detection was absorptimetric at 276nm. The method was linear in the concentration range of 10-35�g/ml (r2=0.9995). The intra and inter-day precision was with in +2% .The assay accuracy was with in 2%. The method was successfully employed in a pharmacokinetic study after an oral administration of a formulation, containing 1000 mg guaifenesin.