Aims Schinus terebinthifolius leaves are used for treating human diseases caused by micro-organisms. This work reports the isolation, characterization and antimicrobial activity of S. terebinthifolius leaf lectin (SteLL). Methods and Results The isolation procedure involved protein extraction with 0·15 mol l⁻¹ NaCl, filtration through activated charcoal and chromatography of the filtrate on a chitin column. SteLL is a 14-kDa glycopeptide with haemagglutinating activity that is inhibited by N-acetyl-glucosamine, not affected by ions (Ca²⁺ and Mg²⁺) and stable upon heating (30–100°C) as well as over the pH 5·0–8·0. The antimicrobial effect of SteLL was evaluated by determining the minimal inhibitory (MIC), bactericide (MBC) and fungicide (MFC) concentrations. Lectin was active against Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa, Salmonella enteritidis and Staphylococcus aureus. Highest bacteriostatic and bactericide effects were detected for Salm. enteritidis (MIC: 0·45 μg ml⁻¹) and Staph. aureus (MBC: 7·18 μg ml⁻¹), respectively. SteLL impaired the growth (MIC: 6·5 μg ml⁻¹) and survival (MFC: 26 μg ml⁻¹) of Candida albicans. Conclusions SteLL, a chitin-binding lectin, purified in milligram quantities, showed antimicrobial activity against medically important bacteria and fungi. Significance and Impact of the Study SteLL can be considered as a new biomaterial for potential antimicrobial applications.