In this paper, we report the synthesis of a new metastable superconducting phase formed during the process of the crystallization of amorphous La72Si28 alloy. As starting material, the La72Si28 amorphous ribbons were prepared from melt by rapid quenching method. The new metastable phase appeared when the amorphous sample was treated at 250℃ for 30 minutes. This phase has a ortborhombic structure with lattice parameters α=9.12l?, b=6.821? and c=3.833?, and exhibits superconducting transition at Tc =3.02 K which is higher than those of all the known La-Si phases.