In the present study, it was aimed to compare of resynchronization with used progesterone (P4) releasing intravaginal device (PRID), with modified ovulation synchronization in cyclic and non-cyclic Holstein heifers. Animals were randomly divided into two groups; Group I (GI, n=87) and Group II (GII, n=88). Fixed-time artificial insemination (FTAI) following modified Ovsynch protocol with PRID insertion, was performed to all animals. In GI, used PRID was reinserted to the same animals, 15 days after the first FTAI (day 25) for 12 days. Pregnancies were detected by ultrasound in all groups on day 37. For resynchronization, prostaglandin (PG) F-2 alpha was applied to non-pregnant animals on day 37. In GI, following 48 hours from PGF(2 alpha) injection, the gonadotropin-releasing hormone was administrated, and after 18 hours the second FTAI was performed. No additional treatments were applied to the nonpregnant animals found in GII, and heifers were taken to the routine service program. In both groups, the second pregnancy diagnosis was performed 27 days after inseminations by transrectal ultrasonography. Pregnancy rates (PR) following the first and overall inseminations in cyclic and non-cyclic heifers (GI and GII) were detected as 66.4% and 52.3% (P>0.05); 76.3% and 59.1% (P>0.05), respectively. In conclusion, the usage of PRID in the Ovsynch and resynchronization protocol resulted in higher PRs of non-cyclic heifers than cyclic heifers. Moreover, this study reveals that the initial P4 levels of non-cyclic animals should be used as a determinant for pregnancy success in dairy heifers.