The　morphological　mechanisms　of　tin　whisker　growth　on　the　surface　of　oxidized　CeSn3　and　ErSn3　precipitates　were　investigated　during　the　aging.　The　results　indicate　that　most　tin　whiskers　have　constant　cross　section　and　regular　shape.　However,　few　irregular　tin　whiskers　with　special　morphologies　are　also　observed,　including　the　spiral　whiskers,　whiskers　with　a　non-constant　cross　section,　branch-type　whiskers　and　joining-type　whiskers.　Since　the　produced　lattice　expansion　of　the　rare　earth　precipitates　oxidization　provides　driving　force　for　the　tin　whisker　growth,　and　the　oxidization　is　extremely　uneven.　Therefore,　the　changes　of　stress　around　the　tin　whisker　root　will　primary　cause　that　results　in　the　growth　of　irregular　tin　whiskers.