Soluble fms-like tyrosine kinase-1 (sFlt-1 or sVEGFR-1) is a tyrosine kinase protein that disables proteins that cause blood vessel growth. Soluble Flt-1 (sFlt-1) is a splice variant of VEGF receptor 1 (Flt-1) which is produced by a variety of tissues.

These proteins act as a receptor of vascular endothelial growth factor (VEGF), a potent angiogenic growth factor. (Another VEGF receptor is KDR).