The objective of this article is to evaluate emmenagogue activity aqueous extract of <i>Cajanus cajan </i>(<i>fabaceae</i>) leaves in rat. 100 g of leaves powder of <i>Cajanus cajan </i>were added 1 liter from distilled water and mixes it was carried to boiling then filtered. The filtrate was dried with the drying oven, the dried filtrate constitutes the aqueous extract (AECc). For the evaluation of emmenagogue activity, the rates in pseudogestation were used. These rates was obtained by coupling nulliparous and pubescent rates with vasectomized rats (rats made sterile by binding of vas deferens). AECc was managed with the amounts from 12,5 to 600 mg/kg of body weight, as well as the misoprostol with the amount of 2 mg/kg of body weight by oral way. The uterus and blood were taken for respectively the determination of the average weight and for the proportioning of progesterone. The results showed a variation of uterus weight as well as a variation of serum progesterone concentration at rate. AECc effect on the progesterone rate at the rate in pseudogestation gave a significant decrease (p<0.001) progesterone rate to amounts 100; 200; 400 and 600 mg/kg bw compared to control. As for amounts 12.5; 25; and 50 mg/kg bw, the aqueous extract decreased the progesterone rate in a nonsignificant way compared to the control. The aqueous extract of <i>Cajanus cajan </i>thus supports the menstruation with the amounts from 100 to 600 mg/kg bw and relieves of the painful rules to amounts 12.5 to 50 mg/kg bw.