Nitric oxide (NO) and polyamines are critical for implantation and development of conceptuses (embryo and extraembryonic membranes), but mechanisms regulating their biosynthesis in uteri and conceptuses are largely unknown. This study determined the effects of the estrous cycle, pregnancy, progesterone, and interferon tau (IFNT) on expression of NO synthases (NOS1, NOS2, and NOS3), guanosine triphosphate (GTP) cyclohydrolase (GCH1, the key enzyme in de novo synthesis of tetrahydrobiopterin, a cofactor for NO production), and ornithine decarboxylase (ODC1) in uterine endometria in cyclic ewes (Days 10–16) and pregnant ewes (Days 10–20). The mRNAs and proteins for NOS1 and ODC1 were most abundant in uterine luminal (LE) and superficial glandular (sGE) epithelia, and abundance was affected by day of estrous cycle and early pregnancy. NOS2, GCH1, and NOS3 mRNAs were detected in very low abundance in uterine epithelia and stromal cells in both cyclic and pregnant ewes. NOS1 mRNA also was expressed very weakly in conceptuses, whereas NOS3 mRNA was abundant in the trophectoderm and endoderm of conceptuses, as were total NOS1 and NOS3 proteins, inhibitory p-NOS1 protein, and stimulatory p-NOS3 protein. GCH1 mRNA was abundant in the trophectoderm and endoderm of conceptuses between Days 13 and 15 of pregnancy and then decreased thereafter, whereas ODC1 mRNA abundance increased in conceptuses between Days 13 and 18 of pregnancy. GCH1 protein was localized primarily in the nuclei of trophectoderm and endoderm, and its abundance decreased after Day 14 of pregnancy, whereas ODC1 protein was more abundant in the trophectoderm than in the endoderm between Days 13 and 18 of pregnancy. Progesterone stimulated NOS1 and GCH1 expression in LE/sGE and glandular epithelia, whereas IFNT inhibited NOS1 expression in these cell types. Thus, biosynthesis of NO and polyamines in ovine uterine endometria and conceptuses is potentially regulated at transcriptional, translational, and posttranslational levels to favor conceptus development and implantation.