Abstract: An LC-MS/MS method was established for the determination and identification of the related substances in telmisartan and amlodipine double layer tablets. Both sampling and HPLC separation of telmisartan and amlodipine were carried out separately using ODS column(250 mm×4. 6 mm, 5 μm)with linear gradient elution. Good resolution of telmisartan and amlodipine and their related substances were achieved. Fourteen related substances of telmisartan were detected and seven of them were elucidated. Two related substances of amlodipine were identified to be the same as those recorded in British Pharmacopoeia.