Objectie: to evaluate the effects on fertility by immunization with anti-idiotypic antibodies to porcine zona pellucida (PZP) antigen. Method: anti-idiotypic antibodies (Ab2) were produced in New Zealand rabbits immunized with 17D3 monoclonal antibodies (mAbs) (IgG, Ab1) to PZP antigen. The antisera were first passed through immuno-affinity chromatography column linked to normal mouse IgG so as to remove the antibody bound to normal mouse IgG The passing elute was then purified by immuno-affinity chromatography using 17D3 mAbs to get the Ab2. Female BALB/c mice, 5-week-old, were grouped and immunized with the Ab2, PZP antigen, target antigen of the Ab1 and normal rabbit IgG, respectively. The treated female mice were mated with male BALB/c mice and sacrificed at gestation day 10. Analyses included ELISA measurement of anti-ZP antibody titer, fetal number determination and evaluation of ovarian histomorphology. Results: the Ab2 appeared as a single protein band by SDS-PAGE. Shown by a competitive inhibition ELISA, the Ab2 specifically bound to the variable region of the 17D3 Ab1. Compared with controls, the female mice immunized with Ab2 showed a decreased pregnancy rate and a statistically significant reduction in fetal numbers. Histological examination of ovaries demonstrated that Ab2 exposure interfered less with follicular development than did exposure to PZP. Conclusion: immunization of female mice with Ab2 to PZP mAbs suppresses fertility and fetal numbers with minimal ovarian pathology.