Cp23 has been identified as one of the immunodominant antigens involved in the immune response to Cryptosporidium parvum infection. Thus, in this study, Cp23 antigen was investigated as a vaccine candidate using the DNA vaccine model in adult interleukin-12 (IL-12) knockout (KO) mice, which are susceptible to C. parvum infection. Our data show that subcutaneous immunization in the ear with DNA encoding Cp23 (Cp23-DNA) cloned into the pUMVCb4 vector induced a significant anti-Cp23 immunoglobulin G1 (IgG1) and IgG2a antibody response and specific in vitro spleen cell proliferation to recombinant Cp23 as compared to control mice. Long-term memory responses were also detected after administration of the Cp23-DNA vaccine. Furthermore, Cp23-DNA vaccination induced a 50-60% reduction in oocysts shedding, indicating a partial protection against C. parvum infection in IL-12 KO mice. However, it is possible that this protective response was nonspecific because mice immunized with vector only also exhibited lower oocyst shedding than the naive controls. These results suggest that DNA encoding for immunodominant C. parvum antigens may provide an effective means of eliciting humoral and cellular responses and possibly in generating protective immunity against C. parvum infections in mammals.