This study was designed to determine the efficiency of two different protocols of estrus synchronization on reproductive performance of postpartum dairy cows. Forty-nine postpartum Holstein dairy cows (days in milk, DIM: 45 days) were randomly assigned to three groups. The first group (CIDR-eCG, n:16) received a controlled internal drug release (CIDR) device for 8 days in conjunction with 500 IU of equine chorionic gonadotropin (eCG) i.m. on the day of CIDR withdrawal. The second group (CIDR-PGF2α, n: 15) received CIDR combined with 500 µg prostaglandin F2α (PGF2α) a day before CIDR withdrawal. The third group (n: 18) served as control. Using CIDR combined with eCG or PGF2α protocols improved ovarian activity as indicated by increasing (P<0.05) total number of follicles and diameter of largest follicles compared to control. Nevertheless, CIDR-eCG protocol was superior in reducing (P<0.05) number of small follicles and increasing (P<0.05) number of large follicles compared to CIDR- PGF2α protocol. The pronounced luteotrophic effect of CIDR-eCG protocol expressed as greater (P<0.05) progesterone (P4) concentration compared with both of CIDR-PGF2α and control groups, between which no significant difference was observed. Both CIDR-eCG and CIDR-PGF2α groups increased (P<0.05) estradiol (E2) concentration compared to that of control. These differences were reflected in estradiol: progesterone ratio (E2: P4) which was lowest (P<0.05) in the CIDR-eCG group and highest (P<0.05) in the control group while the CIDR-PGF2α group was intermediate. Furthermore, the two estrus synchronization protocols successfully reduced (P<0.05) the days to first estrus (DFE) compared to control (56.33 and 61.25 vs. 84.6 days respectively). Nevertheless, the reproductive performance including estrus rate (ER), conception rate (CR), conception failure (CF) and number of services during 100 DIM (NS100) were not different between estrus synchronized and control groups. However, pregnancy rate (PR) achieved the highest (P<0.05) value in the CIDR-eCG protocol. In conclusion, usage of CIDR-eCG protocol alleviated the deterioration in reproductive traits of postpartum Holstein dairy cows through increasing the numbers of large follicles and P4 concentration and reducing day to first estrus and E2:P4 ratio. The reduction in E2:P4 ratio in the CIDR-eCG protocol was reflected in increasing (P<0.05) pregnancy rate compared to the CIDR-PGF2α and control groups.