From　the　reaction　of　Mo3S4(mu-dtp)(dtp)(3)(H2O　)　(I)　(dtp　=　diethyldithio-phosphanato)　with　2,2＇-bipyridine,　the　product　Mo3S4(mu-dtp)(eta(2)-dtp)(2)(eta(1)-dtp)(bpy)　(II)　has　been　isolated,　and　characterized　by　X-ray　crystallography.　Crystal　(II)　belongs　to　triclinic　system　in　space　group　Pr　with　crystallographic　parameters　as　following:　a=13.638(3)angstrom,　b=13.983(3)angstrom,　c=14.699(2)angstrom,　a　=95.57　degrees,　beta=91.87　degrees,　gamma=117.40　degrees;　V=2467(2)angstrom(3),　Z=2,　Dc=1.767g.cm(-3),　final　R=0.069,　R-w=0.076.　The　results　of　the　structure　determination　show　that　the　coordinated　H2O　ligand　and　one　of　sulphur　atoms　of　dtp　on　the　Mo(3)　atom　of　cluser(I)have　been　substituted　by　2,2＇-bipyridine　ligand.　lt　has　been　pointed　out　that　the　ligand　substitution　reaction　reported　here　is　closely　correlated　with　the　existence　of　loosely-coordinated　site　in　cluster(I),In　addition,the　other　types　of　substitution　reactions　of　Uganda　are　also　discussed,