<i>Rhipsalis baccifera</i> (Sol.) Stearn is a typical cactus from tropical regions with wide geographic distribution, and its therapeutic potential is not yet fully understood, such as antitumoral property. Thus, this study evaluated the cytotoxic ethanolic extract of <i>R. baccifera</i> (EERB) and its antitumor activity against Erlich's tumor in mice. The EERB was obtained, and its phytochemical profile was filed by thin-layer chromatography. The toxicity was evaluated in vitro and in vivo using the microcrustacean<i> Artemia salina</i> Leach and mice. The lethal dose was determined after implantation of a tumor cell suspension, with subsequent treatment with EERB (200 mg/kg and 100 mg/kg) 48h after implantation. These values represent the tenth part of the DL₅₀ and CL₅₀, respectively. The presence of phenols, tannins and triterpenes were demonstrated in the phytochemical results. Toxicity was dose-dependent, and the tumor inhibition was 84.1% and 75.8% at doses of 200 mg/kg and 100 mg/kg, respectively. We can highlight that the growth of Erlich's carcinoma suffered inhibitory effects against the EERB. EERB was found to have low acute toxicity and a high potential for use in antitumor therapy. Thus, new studies involving pre-clinical and clinical analyses of the extract are essential to determine the safe dose.