Objective: To investigate the detecting method and diagnostic value of the tumor marker colorectal carcinoma associated large external antigen (LEA) for colorectal carcinoma. Methods: Monoclonal antibody ND-1, which can recognize LEA, was labeled with biotin aminocaproylhydrazide (BACH) and horseradish peroxidase (HRP) respectively. One step sandwich ELISA Kit for detecting LEA in serum was developed by the biotinylated antibody and enzyme conjugation. The validity and reliability of the kit were evaluated by sera selected from clinic. Results: the OD405 of healthy group was 0.056± 0.038, and that of patients was 0.553± 0.441. The difference between the two groups was significant (P