Objective: The objective of this method was to develop a simple, sensitive, rapid reversed-phase high-performance liquid chromatography (RP-HPLC) and applied for determination of tiemonium methyl sulfate (TIM) in bulk, pharmaceutical formulations with stability-indicating studies. Methods: The stability-indicating capability of this method had been established by subjected TIM to several stress conditions of acidic, basic, oxidative, freezing, heating, photolytic, and catalytic degradation. Results: Good separation between the target analyte and its degradation products without any interference referring to specificity and selectivity of this method had been reported. Reversed-phase C18 Kinetex® column (100 mm × 4.6 mm I.D., 2.6 µm), isocratic mobile phase composed of an aqueous solution adjusted to pH 2.3 by 0.1% orthophosphoric acid-acetonitrile (80:20, v/v) at 0.8 ml/minutes flow rate were used. The assay showed good linearity over the concentration range of 1-25 µg/ml with a correlation of coefficient >0.999 and with a detection limit of 0.249 µg/ml and a quantitation limit of 0.755 µg/ml. Results of the analysis were validated statistically by recovery studies. Conclusion: Validated stability-indicating RP-HPLC has been developed for estimation of TIM in its pure and commercial forms in addition to good separation from its degradation products within reasonable time