AbstractA phosphine gold(I) and phosphine‐phosphonium gold(I) complexes bearing a fluorescent coumarin moiety were synthesized and characterized. Both complexes displayed interesting photophysical properties: good molar absorption coefficient, good quantum yield of fluorescence, and ability to be tracked in vitro thanks to two‐photon imaging. Their in vitro and in vivo biological properties were evaluated onto cancer cell lines both human and murine and into CT26 tumor‐bearing BALB/c mice. They displayed moderate to strong antiproliferative properties and the phosphine‐phosphonium gold(I) complex induced significant in vivo anti‐cancer effect.