Introduction: The identification of Irregular Antibodies (AI) is a vitally important process for any blood sample that requires a transfusion. For this reason, pre-transfusion tests such as ABO, Rh classification and cross-matching are recommended. Objective: To identify the prevalence of AI in transfused patients from the zonal fractionation center of the province of El Oro, 2022-2023. Methods: A descriptive, retrospective, non-experimental, analytical, and cross-sectional study was conducted. For tracking, the ID-card Liss/coombs card with 6 microtubes containing anti-IgG and anti-C3d within the gel and the ID-Diacell I-II-III reagent were used. In addition, the panel of 11 cells and phenotypes of the Rh factor (anti-C, anti-E, anti-c, anti-e, and anti-K) from the same commercial house were used for identification. Results: The prevalent antibody was anti-E with 16 cases (28.6%), having a higher frequency in females (62.5%) and in patients over 45 years of age (21.5%). Conclusion: The prevalence of AI in transfused patients from the fractionate center of the province of El Oro is like that reported in other articles. Knowing the AI identification allows for the correct phenotyping of the Rh system in a routine manner and thus decrease the risk of adverse reactions associated with transfusions.