colitis is caused by a cytotoxin produced by the anaerobic bacteria on the epithelial cells of the large intestine, particularly toxin B (Tcd B). Current toxin assays have proven to be insensitive and have thus been ruled out from diagnostic purposes. Therefore, Tcd B detection via sandwich-type chemiluminescent immunoassay was proposed as a straightforward approach with potential diagnostic applicability. Here, two high-affinity anti-Tcd B monoclonal antibodies were successfully identified and implemented in a fully-automated magnetic-particle-based chemiluminescent immunoassay (CLEIA). In this test, toxin B was sandwiched between the anti-toxin B antibody-coated magnetic particles and alkaline phosphate-labeled anti-toxin B antibodies. Compared with traditional techniques, the proposed immunoassay demonstrated high sensitivity for toxin B identification and was further optimized to achieve a linear response ranging from 0.12 to 150 ng/mL with a limit of detection (LOD) of 0.47 ng/mL. Importantly, the entire process could be completed in less than 30 minutes. The proposed assay was used to detect toxin B in 104 randomly-selected human stool samples and delivered similar results to those of a commercial ELISA kit, highlighting its great potential for rapid and efficient toxin B determination in human stool specimens.