The aim of this study was to develop stealth liposomes containing barbatic acid (BA) and to evaluate their antitumor activity in Swiss mice. Conventional liposomes (BA-CL) and stealth liposomes (BA-SL) were produced using the lipid film hydration method. Cytotoxicity was evaluated against ascites cells from experimental Sarcoma-180 (S-180) tumors and undifferentiated J774. A1 macrophage cells. The internalization of AB-CL and AB-SL by S-180 cells was investigated by fluorescence microscopy. The evaluation of antitumor activity was performed against the experimental S-180 solid tumor. After preparation, the BA-CL and BA-SL formulations had mean diameters of 115.6 ± 5.88 nm and 109.3 ± 2.82 nm and encapsulation rates of 90.66 ± 4.57% and 95.15 ± 5.34%, respectively, and remained stable for at least 90 days when stored at 4 °C. For J774. A1 cells (healthy), the IC50 was determined only at a dose of 40 μg/mL. Cell uptake was most intense after 3 h of incubation. Tumor inhibition was 21.79%, 30.26%, and 42.96% for BA, BA-CL, and BA-SL, respectively. Animals treated with BA-SL exhibited greater tumor inhibition and increased survival time compared to animals treated with the BA suspension. These findings demonstrated that the encapsulation of BA in liposomes increased its antitumor activity. Keywords: Lichens; Barbatic acid; Liposomes; Cytotoxicity; Antitumor.