Objective: The aim of the study was to characterize the role of EP1 in unexplained recurrent spontaneous abortion . Methods: A total of 48 induced aborters (Control Group ) and 37 recurrent spontaneous aborters(RSA Group) were enrolled. PGE2 receptor EP1 in MSMC at mRNA level was analysed using reverse transcription PCR and real-time PCR. Cell contraction was acquired with microscope analysis system in MSMC of URSA and Control group. EP1 siRNA or negative control siRNA treatment was operated in URSA MSMC. Results: In total，the level of EP1 was found increased in RSA group, consistently, cell contraction was found increased in RSA Group in comparison to controls. Knocdown of EP1 significantly decreased the level of cell contraction in URSA MSMC. Conclusions: Results suggest that upregulation of EP1 in unexplained recurrent spontaneous aborters, which probably mediates increased uterine contraction