Abstract. The objective of this study was to investigate the possibility of increasing ovulation rate in Norduz sheep by immunization against inhibin-based peptide immunogens. A total of 18 primiparious Norduz ewes were used for this experiment. Eight ewes have received two times inhibin α-subunit 1-32 porcine vaccine with 3 weeks interval. The rest was kept as control. Antibody binding test by standard ELISA method did not provide reliable information. However, ultrasonographic inspection showed that significantly high number of follicle with 5 mm and larger diameter (P<0.01) has developed in immunized ewes. Moreover, 3 of immunized ewes have lambed twin. However, twin birth was not observed in control group.