A sensitive gradient reverse phase high performance liquid chromatography (HPLC) method development fo r identification and quantification of impurities in pharmaceutical products is a challenging and innova tive activity. The present investigation aims to the identificatio n of new unknown impurity of Tolterodine tartrate f ormed in stability samples of the drug product at a level up to 0.5% by using a stability indicating HPLC metho d. This impurity molecular weight was identified by LC-MS a nd characterized by various spectroscopic technique s such as 1 H NMR, 13 C NMR, LC/MS/MS, elemental analysis and FT-IR. Base d on the data obtained from spectroscopic tools, the impurity was named as, 6-methyl-4-phenylchroman -2-ol. The structure of this impurity was also esta blished unambiguously, prepared by isolation and co-injecte d into HPLC to confirm the retention time. To the b est of our knowledge, this impurity has not been reported else where. Structural elucidation of the impurity by sp ectral data is discussed in detail.