Background: Fertility plays great role in animal reproduction since high quality semen improves sheep industry reproduction. The current worldwide data revealed the closely related of CNP to reproductive function of rams. Aims: Evaluation the effect of CNP on cooled sperms using the traditional and molecular assays. Methods: Totally, 20 testicular samples were collected, processed to obtain the semen samples and divided into two parts; one treated with the suitable dose of CNP and the otherserved as a control. Sperm samples of both groups were cooled for 3 days and tested at 0 0h, 24h, 48h and 72h. Results: The findings revealed that the suitable dose of CNP-treated sperms was 0.0110-13. Values individual motility, live sperms and sperm concentration were reduced significantly in CNP-24h, CNP-48h and CNP-72h when compared to control; however, abnormal sperms were increased in both control and CNP groups at 24h, 48h and 72h when compared to values of 0h. Concerning turbidmetric analysis, significant reduction in values of lag time was observed in CNP when compared to control at all times of cooling intervals. In both CNP and control groups, motility index was decreased at 24h, 48h and 72h when compared to 0h. For velocity, significant increases were showed in CNP compared with control at all cooling intervals. However, values of both groups were increased significantly at 24h, 48h and 72h times when compared to 0h. FRMS of CNP was elevated at 0h and decreased at 24h, 48h and 72h when compared to control. Expression of hNPR-B gene was reduced gradually in sperms of CNP and control groups at times of cooling intervals. Conclusion: For our knowledge, this first Iraqi study targets the effect of CNP on epididymal sperms of rams. However, changes occur after excessive CNP exposure remains unclear, and toxicological profile of CNP required furthermore supplements.