Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) play crucial roles in mammalian reproduction by mediating steroidogenesis and gametogenesis. Gonadal steroid hormones influence gonadotropin production via feedback to the hypothalamus and pituitary. We previously demonstrated that progesterone and testosterone can stimulate expression of the FSH -subunit gene in immortalized gonadotrope-derived LT2 cells. Herein, we investigate how these gonadal steroids modulate activin signaling in the gonadotrope. Co-treatment of LT2 cells or mouse primary pituitary cells with steroids and activin results in a synergistic induction of FSH gene expression. This synergy decreases when DNA-binding mutations are introduced into the steroid receptors or when mutations that reduce steroid hormone responsiveness are introduced into the FSH promoter, indicating that synergy requires direct DNA binding of the steroid receptors. Furthermore, classical activin signaling via Smad proteins is necessary for this synergy. In addition, these steroid receptors physically interact with Smads and are sufficient for the synergism to occur on the FSH promoter. Disruption of Smad binding to the promoter with a Smad protein lacking the DNA-binding domain or an FSH promoter containing mutated activin-response elements prevents the synergistic enhancement of FSH transcription. Collectively, our data demonstrate that the molecular mechanism for gonadal steroid hormone action on the FSH promoter involves crosstalk between the steroid and activin signaling pathways. They also reveal that this synergism requires binding of both the steroid receptors and Smad proteins to their cognate DNA-binding elements and likely involves a direct protein-protein interaction between the two types of transcription factors.