Abstract: The present study investigated the diuretic activity of the methanolic extract of Cosmos sulphurous in Wistar albino rats using the Lipschitz test, with Furosemide (10 mg/kg, p.o.) as the reference standard. Animals were divided into five groups (n=6) and urine was collected for 5 hours post-dosing in metabolic cages. Diuretic response was assessed by measuring total urine volume, urinary electrolyte excretion (Na⁺, K⁺, Cl⁻), diuretic index, saluretic index, natriuretic index, and ion quotient. The extract produced a significant, dose-dependent increase in urine output with diuretic indices of 1.61, 2.06, and 2.55 at doses of 250, 300, and 500 mg/kg, respectively, compared with control (1.0) and approaching the standard (2.9). Enhanced excretion of sodium, potassium, and chloride with mild reductions in their serum levels indicated marked saluretic and natriuretic effects. Serum total protein showed only a slight reduction within physiological limits, suggesting the absence of harmful protein depletion. Phytochemical screening revealed the presence of alkaloids, glycosides, flavonoids, phenols, saponins, tannins, steroids, and amino acids, which may contribute to the observed activity. The findings demonstrate that Cosmos sulphurous possesses significant diuretic potential comparable to the standard drug and supports its traditional use as a natural diuretic agent.