A　size-dependent　Kirchhoff　micro-plate　model　is　developed　based　on　the　strain　gradient　elasticity　theory.　The　model　contains　three　material　length　scale　parameters,　which　may　effectively　capture　the　size　effect.　The　model　can　also　degenerate　into　the　modified　couple　stress　plate　model　or　the　classical　plate　model,　if　two　or　all　of　the　material　length　scale　parameters　are　taken　to　be　zero.　The　static　bending,　instability　and　free　vibration　problems　of　a　rectangular　micro-plate　with　all　edges　simple　supported　are　carried　out　to　illustrate　the　applicability　of　the　present　size-dependent　model.　The　results　are　compared　with　the　reduced　models.　The　present　model　can　predict　prominent　size-dependent　normalized　stiffness,　buckling　load,　and　natural　frequency　with　the　reduction　of　structural　size,　especially　when　the　plate　thickness　is　on　the　same　order　of　the　material　length　scale　parameter.　(C)　2011　Elsevier　Masson　SAS.　All　rights　reserved.