The　effects　of　organic-inorganic　cage-type　polyhedral　oligomeric　silsesquioxane　(POSS)　on　the　whisker　formation　behavior　of　Sn-based　lead-free　solders　were　investigated.　Pure　Sn　and　Sn3.0Ag0.5Cu　(SAC305)　solders　were　used　as　solder　matrix,　and　the　composite　solder　was　fabricated　with　3　wt%　POSS　trisilanol　addition.　The　samples　were　tested　under　thermal　cycling　to　accelerate　whisker　growth,　and　the　temperature　range　varied　between　-40　degrees　C　and　85　degrees　C.　The　surficial　evolution　and　interfacial　microstructure　were　observed.　The　results　indicate　that　POSS　would　stabilize　solder　matrix　under　thermal　cycling　condition.　Meanwhile,　the　strength　and　microhardness　of　solders　are　improved　by　POSS　significantly,　which　consequently　reduce　the　deformations　in　the　solders　caused　by　deformations,　and　inhibit　whisker　formation　eventually.