Two　polyoxometalate-phosphonate　compounds　with　the　formular　(TBA)2(Hbiz)2　[(C3H5O2P)2Mo5O21]•05H2O　(1)　and　[Ni(2,2′bpy)3]2[(C6H5P)2Mo5O21]•3H2O　(2)　(TBA=tetrabutylammonium,　biz=benzimidazole,　bpy=bipyridine)　have　been　synthesized　under　hydrothermal　condition　and　structurally　determined　by　single-crystal　X-ray　diffraction.　Compound　1　and　2　are　Strandberg-type　polyoxometalate.　The　compounds　were　characterized　by　various　means　containing　elemental　analysis,　PXRD,　IR　and　thermal　gravimetric　analysis.　Additionally,　their　photocatalytic　degradation　properties　toward　rhodamine-B　are　investigated.　Compound　2　as　catalyst　has　higher　photocatalytic　degradation　of　RhB　than　1　due　to　its　larger　porosity.　Results　of　the　experiment　on　antitumor　activities　in　vitro　showed　that　two　compounds　inhibited　five　different　human　cancer　cells　(gastric　cancer　cells,　HGC-27　and　SNU668;　liver　cancer　cells,　Huh7;　and　colon　cancer　cells,　HCT116　and　SW480)　demonstrated　dose　dependency　and　selectivity.　The　relationship　between　structure　and　biology　activity　indicate　that　inorganic　and　organic　segments　may　influence　the　antitumor　activity,　the　introduction　of　biz　and　3-phosphonopropionic　acid　into　P2Mo5　can　make　compound　1　better　antitumor　activities.　©　2021