The objective of this study was to investigate the efficacy of used controlled internal drug release devices (CIDR-G) on estrous synchronization in ewes. This investigation was conducted in 58 fat-tailed ewes during the non-breeding season. Ewes were divided in to four groups. In Group I, CIDR-G devices were inserted to vagina for 12 d (CIDR group). In Group II, previously used CIDR-G devices were inserted into the vagina for 12 d (U-CIDR). After the intravaginal devices had been removed 500 IU equine chorionic gonadotropin (eCG) was injected intramuscularly (i.m.) into ewes of the CIDR and U-CIDR groups. Ewes in Group III (eCG group), 500 IU eCG was injected im. Ewes in Group IV, served as control and received an injection of 3 mL 0.9% NaCl ( C Group). None of the control ewes expressed estrus. It was found that, 13/15 (86.67%), 10/15 (66.67%) and 1/13 (7.69%) ewes expressed estrus in CIDR, U-CIDR and eCG groups, respectively. The pregnancy rates in the CIDR, U-CIDR and eCG groups were 8/15 (53.33%), 9/15 (60%) and 1/13 ( 7.69%) at first breeding, respectively. The interval from eCG application to onset of estrus was 42.6+/-1.01, 40.13+/-1.35 and 74 h in the CIDR, U-CIDR and eCG groups, respectively. Average progesterone (P4) levels during P4 treatment were 3.28+/-0.28 and 2.62+/-0.14 ng/ml in the CIDR and U-CIDR groups, respectively. It is concluded that, CIDR-G that have been previously used for 12 d could be used for the synchroniation of estrus in ewes during non-breeding season.