It　is　known　that　rare-earth　elements　exhibit　high　chemical　activity　and　adding　trace　amount　of　rare-earth　(RE)　in　the　solder　can　significantly　improve　the　properties　of　solder　alloy.　However,　RE-phases　with　large　size　precipitated　in　the　Sn-3.8Ag-0.7Cu-1.0　RE　solder　alloy　are　oxidized　when　exposed　in　air,　tin　whiskers　growing　rapidly　on　the　surface　of　the　oxidized　RE-phases.　Tin　whisker　growth　on　the　surface　of　the　oxidized　YSn3　phase　is　investigated　at　room　temperature　and　150C　storage　in　air　respectively.　The　results　indicate　that　tin　whiskers　grow　slowly　and　distribute　unevenly　on　the　surface　of　the　oxidized　YSn3　phases　during　room　temperature　storage　in　air,　but　tin　whiskers　grow　rapidly　and　the　YSn3　phase　is　extruded　around　even　solder　matrix　during　150C　storage　in　air.