Crystalline (3Z,S3)-5-(hydroxymethyl)-1-[(2′-methyl-1,1′-biphenyl-4-yl)carbonyl]pyrrolidin-3-one O-methyloxime is disclosed. A pharmaceutical composition containing the crystalline compound and methods for treating conditions related to the OT-R activity, such as preterm labor, and for increasing embryo implantation rate in a mammal undergoing embryo transfer, comprising administering the crystalline compound are also disclosed.