The anti-colorectal cancer monoclonal antibody CO17-1A (mAb CO), which recognizes the tumor-associated antigen EpCAM, was expressed in transgenic Arabidopsis plants. PCR and western blot analyses showed the insertion and expression of heavy chain (HC)/HC fused to the KDEL ER retention modif (HCK) and light chain (LC) of mAb CO and mAb CO with HCK (mAb COK) in Arabidopsis transformants. Both plant-derived mAbP CO and mAbP COK were purified from a biomass of approximately 1,000 seedlings grown in a greenhouse. In sandwich ELISA, both mAbP CO showed a slightly higher binding affinity for the target, EpCAM, compared to mAbM CO. In cell ELISA, both mAbsP COs showed binding affinity to the human colorectal cancer cell line SW480. Furthermore, mAbM CO, mAbP CO, and mAbP COK exhibited dose and time-dependent regression effects on SW480 cells in vitro. In summation, both mAbP CO and mAbP COK, expressed in Arabidopsis, recognized the target antigen EpCAM and showed anti-proliferative activity against human colorectal cancer cells.