Introduction: Rectal adenocarcinoma is the most common tumor of the lower digestive tract of the dogs, affecting the quality of life. Electrochemotherapy (ECT) is a novel drug delivery system that enhances the intracellular delivery of low-permeability cytostatic drug through the transient permeabilization of the cell membrane. This study aimed to evaluate ECT as a treatment for colorectal adenocarcinoma in dogs Experimental procedure: Twelve dogs diagnosed with rectal adenocarcinoma were included. For each patient, data recorded included, breed, sex, tumor size, number of treatment sessions, clinical response, recurrence, disease-free interval and post treatment complications. The therapeutic protocol consisted in intravenous administration of Bleomycin (15,000 IU/m2). Traction points were placed in the rectal mucosa to facilitate exposure of the lesion to be treated. Eight minutes after drug administration, electric pulses were delivered using a Biotex EPV200 electroporator (Argentina). A train of eight monophasic pulses (1000V/cm, 5000Hz) was applied using needle and plate electrodes. Results: This is the first study in dogs evaluating ECT for rectal adenocarcinoma. Most tumors were pedunculated and smaller than 1cm (9/12).; the remaining were broad-based, with one case involving nearly the entire rectal circumference. All lesions were located within 3cm of the anus. All dogs (12/12) underwent a single treatment session, achieving a 100% complete response rate. Ten of twelve dogs remained disease-free at the end of the study; one died of unrelated causes after two years, and two showed local recurrence (at 308 and 688 days, respectively), the latter successfully retreated and disease-free to date, with survival exceeding 1350 days. Observed complications included local inflammation and tenesmus; pain and constipation were reported in two cases. Conclusion: Bleomycin delivered by electroporation for rectal adenocarcinoma in dogs proved to be effective and can be considered a first-line alternative to surgery. A comprehensive medical management plan is recommended to address post treatment complications.