Tin　whisker　growth　on　the　surface　of　ErSn3　phase　was　investigated　during　air　and　vacuum　aging　of　ErSn3,　respectively.　The　results　indicate　that　tin　whisker　growth　occurs　on　the　surface　of　the　oxidized　ErSn3　phase　during　air　aging.　Moreover,　the　growth　rate　is　slow　and　the　distribution　is　uneven　during　room　temperature　aging;　on　the　contrary,　the　growth　rate　of　tin　whiskers　is　fast　and　the　distribution　is　even　during　150　degrees　C　aging;　however,　no　tin　whisker　is　found　on　the　surface　of　ErSn3　phase　during　vacuum　aging.　The　volume　expansion　which　is　caused　by　diffusion　of　oxygen　atoms　into　ErSn3　lattice　during　oxidization　in　air　produces　compressive　stress　that　provides　the　driving　force　for　tin　whisker　growth;　thus　tin　whisker　growth　happens　during　air　aging　and　no　whisker　is　found　during　vacuum　aging.