In recent years, efforts to treat cancer by improving the immune function of patients have received a great deal of attention. As part of the immune system, complement is also under such evaluation. Among the many components of the complement system, complement decay accelerating factor (CD55 or DAF) is known to inhibit complement‑mediated cell lysis. However, little is known about the role of CD55 in terms of cancer therapy. The present study aimed to demonstrate that increased levels of CD55 are strongly correlated with the progression of colorectal cancer. A novel CD55 chimeric monoclonal antibody was developed that may boost the immune response, thereby suppressing cancer. The CD55 antibody treatment activated complement and therefore suppressed the proliferation, invasion and migration of colorectal cancer cells. This tumoricidal activity is partly explained by the inflammatory response via the activation of proinflammatory cytokines. In addition, the CD55 antibody treatment synergistically enhanced the tumoricidal activity of 5‑FU in colorectal cancer cells, suggesting that combined treatment may be a better strategy in colorectal cancer therapy.