The preparations of herbal nature are wide popular for the additional and prolonged stimulation of diuresis. The complex herbal preparation Urolesan (joint-stock company “Galichpharm”, Ukraine) is applied in the practical medicine, including the urology, for more than 50 years. The diuretic action of the sublingual drops of Urolesan in the most spread type of stone formation – calcium urolithiasis, in the region with hot and dry climate as the diuretic drug for the prolonged application, are not yet studied. It has been performed the analysis of 36 patients with uncomplicated calcium urolithiasis (So, Sres, Rmo categories) and with calcium preurolithiasis. Urolesan in the dosage of 8-10 drops has increased the dieresis for 15.1%. The preparation has mild diuretic action (the increase of dieresis less than 25%) in this dosage. In the dosage of 15-20 drops, Urolesan has increased the dieresis for 34.7 % - the moderate diuretic effect (dieresis has been increased more than 25%, but less than 50%). The mechanism of the diuretic action is: the increase of GF (on the average for 40.7 % from baseline) and the decrease of CR (for 57.7 % from baseline).