Semicarpus anacardium ‘Marketing Nut’ is a tropical flowering plant widely distributed in India. Semicarpus anacardium are widely used for its therapeutic potential as immunomodulatory and in folklore the plant material is reported in the treatment of diuretic. Since, the diuretic activity of these plant materials has not been investigated in scientifically controlled studies; the aim of the present study was to evaluate the diuretic potential of milk extracts of Semicarpus anacardium seed in normal rats after acute and sub-chronic oral administration. Milk extracts of Semicarpus anacardium seed (150 and 300 mg/kg) along with the reference drug, furosemide (10 mg/kg) were administrated orally to male Wistar rats for 8 subsequent days and their urine output was quantitated at several intervals of time after the dose. Several other parameters such as urinary electrolyte concentration, plasma electrolyte concentration and creatinine clearance were also measured by flame spectrophotometry and Jaffe alkaline picrate method. After administration of single dose of the milk extracts of Semicarpus anacardium seed, urine output significantly showed equivalent increment at all time points, and at 24 h after the dose, the total volume of urine excreted was highest in furosemide followed by plant extracts and control group. Both extracts increased the urinary levels of Na+ and K+, to about the same extent, while furosemide increased urinary levels of only Na+ and decreased urinary K+. Despite changes in urinary excretion of the electrolytes, plasma Na+ and K+ levels were not affected by any of the substances. The present study supports the ethnomedical use of Semicarpus anacardium seed for their diuretic effect.