Abstract The objective of the present investigation was to determine the effect of the ethanolic extract concentrations of Piper angustifolium leaves "matico" on the growth of Proteus mirabilis under laboratory conditions. To obtain the ethanolic extracts of leaves of P. angustifolium "matico", 38 g of leaf powder were distilled in the soxlet equipment with 200 ml of 95% ethanol, the obtained distillate was dried with thermal air and all the obtained it was diluted in 10 ml of twenn 80%, obtaining a stock solution, then dilutions were made (10, 15, 20, 25 and 30 mg / ml). The inoculum of P. mirabilis was prepared with a turbidity level of tube No. 0.5 on the Mc Farland scale and was seeded on Muller Hinton agar; To evaluate the effect of the extract, the method originally described by Kirby-Bauer with Watman No. 4 paper discs of 7mm diameter was used in which 30 ul of each extract diluti...