Steroid-induced osteonecrosis of the femoral head (SONFH) develops with early microvascular injury, but the systemic signals connecting glucocorticoid exposure to the femoral head remain incompletely defined. We examined whether intestinal epithelial Piezo1–TPH1–serotonin signaling contributes to this process. A glucocorticoid-induced SONFH model was studied in male C57BL/6 mice (8–10 weeks old), using pharmacological inhibition of peripheral serotonin synthesis, intestinal epithelial-specific Piezo1 deletion, micro-computed tomography, histological and vascular analyses, bone microvascular endothelial cell (BMEC) assays, and independent public transcriptomic datasets. Glucocorticoid exposure increased intestinal Piezo1 and TPH1 expression and circulating serotonin, together with loss of CD31^hiEMCN^hi type H vessels and trabecular deterioration. Inhibiting peripheral serotonin synthesis reduced vascular and structural injury. Intestinal epithelial Piezo1 deletion blunted TPH1 upregulation, preserved femoral-head microvasculature, and improved trabecular architecture. In BMECs, serotonin impaired tube formation and increased Bax-, Caspase-3-, and NLRP3-associated signaling; intestinal Piezo1 deletion reduced the corresponding injury signals in vivo. Intestinal epithelial Piezo1–TPH1–serotonin signaling therefore contributes to SONFH-associated microvascular injury in this model.