Contents: The function of prion-like protein Doppel was suggested to be related to male fertility. In this study, the importance of ovine Doppel polypeptide on spermatozoa capacitation and fertilization was evaluated. After refolding, recombinant Doppel (rDpl) was supplemented with different concentrations (40, 80 or 190ng/ml) to ovine spermatozoa during the capacitation process. In experiment 1, post-thawed ovine spermatozoa were incubated with different concentrations of rDpl during 1h for swim-up, and changes in sperm motility, concentration, vigour, viability and capacitation were monitored (10 replicates). In experiment 2, the fertilization ability of post-swim-up spermatozoa incubated as above was tested through heterologous fertilization of bovine in vitro matured oocytes (n=423, three replicates). Regardless of dosage, rDpl improved (p≤0.03) spermatozoa viability. Sperm individual motility and vigour were the highest (p≤0.04) for the group receiving 190ng/ml rDpl. Sperm supplemented with the highest doses of rDpl achieved higher (p=0.02) fertilization rates (56.0±3.0%) than control (39.1±2.2%) and 40ng/ml rDpl (39.8±2.7%). Preliminary data suggest that Doppel protein may enhance in vitro spermatozoa fertilizing ability.