The growing antibiotic resistance among pathogenic bacteria is a major problem in clinical settings, leading microbiologists to search for new compounds with antimicrobial activity. Medicinal plants have recently received increasing attention as their antimicrobial compounds offer attractive candidates for fighting resistant bacteria. Eucalypt trees have been used by Australian aboriginals for thousands of years for treatment of bowel inflammation, diarrhoea, sores, skin lesions, scabies, cramps, sore throat and coughs. These plants exude a polyphenol- and tannin-rich gum (the kino) but their biological activities have not been fully investigated. We screened crude ethanolic extracts of kinos from two species of eucalypt, Corymbia citriodora and C. torelliana, and their hybrid, C. torelliana × C. citriodora, against five bacteria, Escherichia coli (ATCC 25922), Salmonella typhimurium (ATCC 13311), Pseudomonas aeruginosa (ATCC 27853), Staphylococcus aureus (ATCC 25923) and Bacillus cereus (ATCC 11788), as well as a wild type Candida albicans and four additional wild strains of Pseudomonas. All three crude extracts showed activity against the tested microorganisms, but kino extract from the hybrid was significantly more active than other extracts against S. typhimurium and C. albicans. The highest antimicrobial activity of the extracts was against the P. aeruginosa. Active crude extracts were not cytotoxic to human epithelial colorectal adenocarcinoma (Caco-2) cells although they caused some morphological changes to these cells after 4 hours of treatment. None of the extracts inhibited biofilm formation by the tested strains. Our results suggest the presence of active compounds with antimicrobial activities in eucalypt species.