Early growth response 1 (Egr1) is an inducible zinc finger transcription factor. Egr1 binds specific GC-rich region. Egr1 mRNA is rapidly and transiently expressed in pre-ovulatory follicles by LH and expressed in decidual cell by estrogen. Progesterone receptor (PR) is a nuclear transcription factor that is induced in granulosa cells of pre-ovulatory follicles following the LH surge. PR regulates ADAMTS1, which downstream gene of PR. In previous study, we observed ADAMTS1 mRNA expression pattern changed in Egr1 KO mice. Therefore, we expected that progesterone receptor gene expression is directly regulated by early growth response 1 in mouse ovarian granulosa cell. We could found the ER binding domain, Egr1 binding domain and CAAT box in PR promoter using the web tool AliBaba 2.1. We construct the PR promoter vectors truncated ER binding domain, Egr1 binding domain, CAAT box, respectively. We also construct the Egr1 expression vector using pcDNA 3.1 (+) vector. Granulosa cells are isolated from female ICR mice after 12h PMSG injection. To confirm the Egr1 overexpression, we performed western blot. For reporter assay, we used Dual-Luciferase reporter assay system. In conclusion, Egr1 may regulate PR expression in granulosa cell.