The hemagglutinating (HA) activity of Cratylia mollis lectin (Cra) was evaluated and the influence of ultrasound and mechanical agitation on its activity examined. The antitumor activity of Cra-loaded liposomes was also investigated. Liposomes were obtained by the lipid thin film method. Physicochemical characterization was carried out and long-term stability of Cra-loaded liposomes assessed. Antitumor activity of Cra-loaded liposomes was investigated against Sarcoma 180 in Swiss mice. The treatment was performed intraperitoneally (7 mg/kg body weight per day) for 7 days. Histopathological analyses of tumor, liver, spleen and kidneys were carried out after treatment of the animals. The results showed that Cra-HA activity is affected under ultrasound exposure. However, Cra was successfully encapsulated into liposomes and the activity of the lectin was preserved despite the use of ultrasound in the liposome preparation. Cra-loaded liposomes were produced with an 84% encapsulation ratio (700 microg/ml) and a tumor inhibition of 71% was achieved. The encapsulation of Cra produced a decrease in its tissue toxicity and improved its antitumor activity. In particular, histopathological analysis revealed that treatment with Cra-loaded liposomes prevented Cra cytotoxicity in the liver and kidney of animals.