The　SiO2　microspheres　with　different　diameters　were　prepared　by　a　seeding　technique　through　adjusting　the　mass　fraction　ratio　of　TEOS　and　silica　sol　in　the　reaction　solution.　The　mesoporous　SiO2/Fe3O4　microspheres　with　size-tunable　hollow　cavity　were　prepared　by　using　the　SiO2　microspheres　of　different　diameters　as　templet.　The　magnetic　mesoporous　SiO2/Fe3O4　hollow　microspheres　were　used　as　the　carriers　to　immobilize　papain,　and　the　effect　of　hollow　cavity　on　papain　immobilization　was　researched　in　detail.　The　results　show　that　the　amount　of　papain　immobilization　increased　with　the　size　of　hollow　cavity　increasing.　The　amount　of　papain　immobilization　washigh(296　mg.g(-1)),　when　the　hollow　cavity　average　size　was　about　330nm.　It　was　indicated　that　the　hollow　cavity　is　a　natural　warehouse　storing　papain　molecules　effectively.　When　the　temperature　was　below　60　degrees　C　and　the　pH　was　from　2　to　8,　the　residual　activity　of　immobilized　papain　still　remained　more　than　60%,　much　higher　than　that　of　free　papain.