A gradient method is developed for the quantitative simultaneous determination of impurities of glimepiride and metformin hydrochloride in the combined –pharmaceutical dosage form. The method is based on high- performance liquid chromatography (HPLC) on a reverse phase column of Waters Symmetry -C8,5μ 4.6 x 250mm thermo stated at 50o C, using a mobile phase of Pentane sulfonic acid sodium salt buffer pH 3.5 and acetonitrile and evaluated for its ability to simultaneously establish the level of known impurities of glimepiride and metformin Hydrochloride active as well as unknown impurities in glimepiride and metformin hydrochloride tablets. The method shows good resolution between glimepiride sulfonamide (GS), glimepiride urethane (GU), glimepiride 3- isomer (GI), metformin related compound A (MA), glimeiride (G),metformin hydrochloride (M) , unknown impurities and formulation excipients of tablets. A gradient program with UV detection at 230nm is used to quantitate all components. The developed method is validated in term of specificity, linearity and range for GS,GU,GI, MA , M and G , accuracy using spiked levels of impurities (80% -120% of the specified limit ) , precision and ruggedness. Limit of quantitation is found to be 1.50 μg mL-1 for M , 0.10 μg mL-1 for G , 0.30 μg mL-1 for MA , 0.24μg mL-1 for GS ,0.10 μg mL-1 for GU and 0.22 μg mL-1 for GI. The proposed method is successfully applied to the pharmaceutical dosage form for the determination and quantitation of known and unknown impurities in M and G tablets without any interference from the excipients.