R-spondin3 (RSPO3), an activator of Wnt/β-catenin signaling, plays a key role in tumorigenesis of various cancers. RSPO3 contains two adjacent cysteine-rich furin-like domains (aa 35-135) with one potential N-glycosylation site (aa 36), followed by a thrombospondin (TSP-1) motif (aa 147-207) and a region rich in basic residues (aa 211-269). RSPO3 is a novel contraction-inducible myokine produced by cultured human myotubes. Human RSPO3 is a paracrine factor that may positively participate in the myogenesis processes of myoblasts and satellite cells. RSPO3 promotes the tumor growth of choriocarcinoma via Akt/PI3K/ERK signaling, which supports RSPO3 as an oncogenic driver promoting the progression of choriocarcinoma. RSPO3 plays a role in the regulation of Wnt (wingless-type MMTV integration site family)/beta-catenin and Wnt/planar cell polarity (PCP) signaling pathways, which are involved in development, cell growth and disease pathogenesis. Genome-wide association studies suggest a correlation of this protein with bone mineral density and risk of fracture.