The postpartum period is considered an important period in the reproductive life of dairy cows.This study was aimed to evaluate the effect of progesterone (P₄)-CIDR supplementation in the course of Ovsynch regimens in postpartum Holstein-Friesian dairy cows. Eighty Holstein Friesian dairy cows were used. All animals were gynaecologically examined for uterine involution and ovarian resumption by rectal ultrasound scan. Those with history of endometritis, caesarean section, dystocia, retained placenta, acute mastitis, lameness or other unhealthy were excluded. Fifty-two cows were cyclic and twenty eights were non-cyclic. Animals were divided into three synch-regimens. The 1^st group (N=27), used as a control, is the ovsynch regimen only in which the animals were treated with GnRH-PGF_2α-GnRH (GPG), the 2^nd group (N=26) in which the GPG was presynchronized with controlled internal drug release (CIDR) device before (CIDR-GPG), and the 3^rd group (N=27) in which CIDR device was incorporated into GPG, after the first GnRH injection (G-CIDR-PG). Blood samples were collected 5 times (day -7, 0, 7, 14 and 50) for measuring P₄ using enzyme-immunoassay (EIA) technique. Ultrasound examinations were performed on days -7, 0, 7 and 9 for following up the ovarian changes, and repeated at 35, 45 and 50 days post-insemination for pregnancy diagnosis. Conception rate was variable among groups. It was increased by 69.23, 51.85 and 40.74% in CIDR-GPG, G-CIDR-PG regimens treated groups and GPG-control group, respectively. The conception rate was higher in the cyclic versus acyclic GPG group (44.4 vs. 33.3 %). On the other hand, acyclic cows were highly responsive than cyclic cows in CIDR-GPG group (70.0 vs. 68.8%) and G-CIDR-PG group (55.6 vs. 50.0%). In conclusion, we recommend that the CIDR-GPG regimen is improving fertility and conception rate in postpartum dairy cows.