Since plant extracts have shown antibacterial activities, Uncaria tomentosa is a medicinal plant used over centuries by the peruvian population as an alternative treatment in different diseases. Many microorganisms are presents in the oral cavity, which, in determined conditions, can become etiologic agents of illnesses. Objectives: The aim of the present study was to evaluate the antimicrobial effects of different concentrations of Uncaria tomentosa over different strains of microorganisms that were isolated from humans oral cavity. Material and methods: A pulverized extract of Uncaria tomentosa was used for in vitro to inhibit the microbial growth by determining minimum inhibitory concentration (MIC). The microorganisms tested were clinical strains isolated of Streptococcus mutans, Sthaphylococcus, Candida albicans, Enterobacteriaceae and Pseudomonas aeruginosa. The concentration of Uncaria tomentosa ranged from 0,25 - 5% in Müeller-Hinton, the minimum inhibitory concentration (MIC) was considered the first dilution where growth did not occur. Results: After analysis descriptive statistics of the data the results showed that Uncaria tomentosa 2% was the MIC , for 8% of Enterobacteriaceae, 52% of S. mutans and 88% of Staphylococcus. The concentrations from the 2% to 5% did not have effects in the growth inhibition of Pseudomonas aeruginosa and Candida albicans. Conclusions: This study shows that a pulverized extract of Uncaria tomentosa has antimicrobial activity against Enterobacteriaceae, S. mutans and Sthaphylococcus.