Among the many species of Brazilian flora with interesting biological properties is Ilex paraguariensis A. St.-Hil. (Aquifoliaceae), popularly known as yerba mate. Emetic, astringent, medicinal and bactericidal properties are popular indications attributed to the species. With this in mind, the aim of this book was to evaluate the antibacterial and antifungal activity of the leaf and branch extracts. The plant material used to produce the extracts was collected in Santo Angelo/RS, the leaves and branches were separated, washed, macerated, crushed with 70% ethanol and then filtered and evaporated. The antimicrobial activity was assessed using the solid medium diffusion technique. The concentration of 100mg/mL showed the best inhibitory effect against all the microorganisms tested. The results obtained proved the marked antifungal activity of the I. paraguariensis extracts, when compared to the inhibition results of the commercial antifungal Fox(R), used as a comparative standard. The positive results indicate that this plant is an alternative for controlling microorganisms in seed storage.