In this study attempts were made to explore effects of the water and alcohol extracts of Junci Herba on the renal function of dogs. The water extract (in a dose 15 mg/kg, i.v.) and alcohol extract (in a dose 1.5 mg/kg, i.v.) elicited a diuretic response and produced a marked diuresis during bicarbonate infusion whereas no diuresis ensues during infusion of hydrochloric acid. The ratios of potassium and sodium excreted in urine $(K^+/Na^+)$, pH of urine, Cosm (osmolar clearance) and $C_{H_2O}$ (free water clearance) increased but hemodynamic states changed little with both extracts. All the observed facts can be best explained on the assumption that Junci Herba inhibits the carbonic anhydrase in the tubule. Thus it produces the effect by increasing urinary potassium and sodium.